<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019eb280-b07a-73cb-a4a4-4e3208d00f1e,g:46453bb7-c84f-4150-960e-0956ede37928-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="irtc-20260630.xsd#CondensedConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019eb280-b143-7213-b84d-7f0fd1462362" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019eb280-b143-778f-be96-eaa0b5e7295e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019eb280-b143-7213-b84d-7f0fd1462362" xlink:to="loc_us-gaap_StatementTable_019eb280-b143-778f-be96-eaa0b5e7295e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019eb280-b143-78eb-a0ee-79163a591e99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019eb280-b143-778f-be96-eaa0b5e7295e" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019eb280-b143-78eb-a0ee-79163a591e99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019eb280-b143-78eb-a0ee-79163a591e99_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019eb280-b143-78eb-a0ee-79163a591e99" xlink:to="loc_us-gaap_EquityComponentDomain_019eb280-b143-78eb-a0ee-79163a591e99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019eb280-b143-783f-be2c-cd28345c0928" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019eb280-b143-78eb-a0ee-79163a591e99" xlink:to="loc_us-gaap_EquityComponentDomain_019eb280-b143-783f-be2c-cd28345c0928" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019eb280-b143-77b9-adfa-1edc9e81950b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019eb280-b143-783f-be2c-cd28345c0928" xlink:to="loc_us-gaap_CommonStockMember_019eb280-b143-77b9-adfa-1edc9e81950b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019eb280-b143-7acd-8ed9-5617fc0a4bc8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019eb280-b143-783f-be2c-cd28345c0928" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019eb280-b143-7acd-8ed9-5617fc0a4bc8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019eb280-b143-7c46-9de1-54485a213c15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019eb280-b143-783f-be2c-cd28345c0928" xlink:to="loc_us-gaap_RetainedEarningsMember_019eb280-b143-7c46-9de1-54485a213c15" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019eb280-b143-7bcc-9f1e-a4be5ed3068b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019eb280-b143-783f-be2c-cd28345c0928" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019eb280-b143-7bcc-9f1e-a4be5ed3068b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019eb280-b143-7dd1-ae21-dfbd0aa98e40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019eb280-b143-783f-be2c-cd28345c0928" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019eb280-b143-7dd1-ae21-dfbd0aa98e40" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eb280-b143-7844-86cc-d09bf0d235d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019eb280-b143-7213-b84d-7f0fd1462362" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eb280-b143-7844-86cc-d09bf0d235d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019eb280-b143-73d6-ae39-bc5fdb7a0ddc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eb280-b143-7844-86cc-d09bf0d235d4" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019eb280-b143-73d6-ae39-bc5fdb7a0ddc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019eb280-b143-7edb-8dd5-d92f9e48db00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eb280-b143-7844-86cc-d09bf0d235d4" xlink:to="loc_us-gaap_StockholdersEquity_019eb280-b143-7edb-8dd5-d92f9e48db00" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019eb280-b143-7128-9a42-a79a7faa283e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eb280-b143-7844-86cc-d09bf0d235d4" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019eb280-b143-7128-9a42-a79a7faa283e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019eb280-b143-7000-9bf8-6b73518b1ff1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eb280-b143-7844-86cc-d09bf0d235d4" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019eb280-b143-7000-9bf8-6b73518b1ff1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019eb280-b143-76e4-b49c-99da15608370" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eb280-b143-7844-86cc-d09bf0d235d4" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019eb280-b143-76e4-b49c-99da15608370" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019eb280-b143-76d0-b6ea-bc396a786d5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eb280-b143-7844-86cc-d09bf0d235d4" xlink:to="loc_us-gaap_NetIncomeLoss_019eb280-b143-76d0-b6ea-bc396a786d5b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019eb280-b143-7aff-af4c-155bd49747fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eb280-b143-7844-86cc-d09bf0d235d4" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019eb280-b143-7aff-af4c-155bd49747fa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019eb280-b143-743e-aba0-0e093938539a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019eb280-b143-7844-86cc-d09bf0d235d4" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019eb280-b143-743e-aba0-0e093938539a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019eb280-b143-7bee-b78d-f70da92ec1eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019eb280-b143-7464-bfe3-caee1e3b547e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_irtc_SummaryOfSignificantAccountingPoliciesLineItems_019eb280-b211-7053-95e2-97be075f1db0" xlink:href="irtc-20260630.xsd#irtc_SummaryOfSignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_SummaryOfSignificantAccountingPoliciesTable_019eb280-b211-7471-81b7-668e41080440" xlink:href="irtc-20260630.xsd#irtc_SummaryOfSignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_irtc_SummaryOfSignificantAccountingPoliciesLineItems_019eb280-b211-7053-95e2-97be075f1db0" xlink:to="loc_irtc_SummaryOfSignificantAccountingPoliciesTable_019eb280-b211-7471-81b7-668e41080440" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019eb280-b211-7cbc-9be9-ebc3f6adcd07" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_irtc_SummaryOfSignificantAccountingPoliciesTable_019eb280-b211-7471-81b7-668e41080440" xlink:to="loc_srt_MajorCustomersAxis_019eb280-b211-7cbc-9be9-ebc3f6adcd07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019eb280-b211-7cbc-9be9-ebc3f6adcd07_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019eb280-b211-7cbc-9be9-ebc3f6adcd07" xlink:to="loc_srt_NameOfMajorCustomerDomain_019eb280-b211-7cbc-9be9-ebc3f6adcd07_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019eb280-b211-7d93-bd91-4feb3327bf85" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019eb280-b211-7cbc-9be9-ebc3f6adcd07" xlink:to="loc_srt_NameOfMajorCustomerDomain_019eb280-b211-7d93-bd91-4feb3327bf85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_CentersForMedicareMedicaidServicesMember_019eb280-b211-7070-9732-ad5a26d8530d" xlink:href="irtc-20260630.xsd#irtc_CentersForMedicareMedicaidServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019eb280-b211-7d93-bd91-4feb3327bf85" xlink:to="loc_irtc_CentersForMedicareMedicaidServicesMember_019eb280-b211-7070-9732-ad5a26d8530d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_HealthcareInstitutionsMember_019eb280-b211-76c0-9c8b-38c739dc4fe5" xlink:href="irtc-20260630.xsd#irtc_HealthcareInstitutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019eb280-b211-7d93-bd91-4feb3327bf85" xlink:to="loc_irtc_HealthcareInstitutionsMember_019eb280-b211-76c0-9c8b-38c739dc4fe5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_ContractedThirdPartyPayorsMember_019eb280-b211-7285-9b5c-22f378defc02" xlink:href="irtc-20260630.xsd#irtc_ContractedThirdPartyPayorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019eb280-b211-7d93-bd91-4feb3327bf85" xlink:to="loc_irtc_ContractedThirdPartyPayorsMember_019eb280-b211-7285-9b5c-22f378defc02" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019eb280-b211-7f6a-b793-67ee025eae55" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_irtc_SummaryOfSignificantAccountingPoliciesTable_019eb280-b211-7471-81b7-668e41080440" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019eb280-b211-7f6a-b793-67ee025eae55" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019eb280-b211-7f6a-b793-67ee025eae55_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019eb280-b211-7f6a-b793-67ee025eae55" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019eb280-b211-7f6a-b793-67ee025eae55_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019eb280-b211-70ed-a3fe-d95aa5adb0cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019eb280-b211-7f6a-b793-67ee025eae55" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019eb280-b211-70ed-a3fe-d95aa5adb0cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_019eb280-b211-73e9-9a6e-1b4a62205946" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019eb280-b211-70ed-a3fe-d95aa5adb0cc" xlink:to="loc_us-gaap_AccountsReceivableMember_019eb280-b211-73e9-9a6e-1b4a62205946" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019eb280-b211-7d28-89d6-152fe3263fe4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_irtc_SummaryOfSignificantAccountingPoliciesTable_019eb280-b211-7471-81b7-668e41080440" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019eb280-b211-7d28-89d6-152fe3263fe4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019eb280-b211-7d28-89d6-152fe3263fe4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019eb280-b211-7d28-89d6-152fe3263fe4" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019eb280-b211-7d28-89d6-152fe3263fe4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019eb280-b211-7dbb-be92-5769f74631ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019eb280-b211-7d28-89d6-152fe3263fe4" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019eb280-b211-7dbb-be92-5769f74631ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditConcentrationRiskMember_019eb280-b211-750f-b909-4392295fa1a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019eb280-b211-7dbb-be92-5769f74631ed" xlink:to="loc_us-gaap_CreditConcentrationRiskMember_019eb280-b211-750f-b909-4392295fa1a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019eb280-b211-7931-a98b-ad6c80f51ced" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_irtc_SummaryOfSignificantAccountingPoliciesLineItems_019eb280-b211-7053-95e2-97be075f1db0" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019eb280-b211-7931-a98b-ad6c80f51ced" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/BUSINESSSEGMENTANDREVENUEScheduleofDisaggregatedRevenuebyPayorTypeandMajorServiceDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#BUSINESSSEGMENTANDREVENUEScheduleofDisaggregatedRevenuebyPayorTypeandMajorServiceDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/BUSINESSSEGMENTANDREVENUEScheduleofDisaggregatedRevenuebyPayorTypeandMajorServiceDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019eb280-b211-7ef2-b662-8ebb70b30863" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019eb280-b211-7301-ab96-ec37018ba7e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019eb280-b211-7ef2-b662-8ebb70b30863" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019eb280-b211-7301-ab96-ec37018ba7e3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019eb280-b211-7105-9fc1-858cf376f73c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019eb280-b211-7301-ab96-ec37018ba7e3" xlink:to="loc_srt_ProductOrServiceAxis_019eb280-b211-7105-9fc1-858cf376f73c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019eb280-b211-7105-9fc1-858cf376f73c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019eb280-b211-7105-9fc1-858cf376f73c" xlink:to="loc_srt_ProductsAndServicesDomain_019eb280-b211-7105-9fc1-858cf376f73c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019eb280-b211-7bf2-81a1-1f446d890d2d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019eb280-b211-7105-9fc1-858cf376f73c" xlink:to="loc_srt_ProductsAndServicesDomain_019eb280-b211-7bf2-81a1-1f446d890d2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_CommercialPayorsMember_019eb280-b211-71d6-a336-cb5f3bc1dd78" xlink:href="irtc-20260630.xsd#irtc_CommercialPayorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019eb280-b211-7bf2-81a1-1f446d890d2d" xlink:to="loc_irtc_CommercialPayorsMember_019eb280-b211-71d6-a336-cb5f3bc1dd78" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_CentersForMedicareMedicaidServicesMember_019eb280-b211-7253-b8fd-41323bcf88de" xlink:href="irtc-20260630.xsd#irtc_CentersForMedicareMedicaidServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019eb280-b211-7bf2-81a1-1f446d890d2d" xlink:to="loc_irtc_CentersForMedicareMedicaidServicesMember_019eb280-b211-7253-b8fd-41323bcf88de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_HealthcareInstitutionsMember_019eb280-b211-77aa-92d8-4c89cc5e89ce" xlink:href="irtc-20260630.xsd#irtc_HealthcareInstitutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019eb280-b211-7bf2-81a1-1f446d890d2d" xlink:to="loc_irtc_HealthcareInstitutionsMember_019eb280-b211-77aa-92d8-4c89cc5e89ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_NonContractedThirdPartyPayorsMember_019eb280-b211-792e-a87b-12b8a732c59c" xlink:href="irtc-20260630.xsd#irtc_NonContractedThirdPartyPayorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019eb280-b211-7bf2-81a1-1f446d890d2d" xlink:to="loc_irtc_NonContractedThirdPartyPayorsMember_019eb280-b211-792e-a87b-12b8a732c59c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019eb280-b211-708c-b332-281941a36068" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019eb280-b211-7301-ab96-ec37018ba7e3" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019eb280-b211-708c-b332-281941a36068" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019eb280-b211-708c-b332-281941a36068_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019eb280-b211-708c-b332-281941a36068" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019eb280-b211-708c-b332-281941a36068_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019eb280-b211-7383-8217-a94ea98aaef1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019eb280-b211-708c-b332-281941a36068" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019eb280-b211-7383-8217-a94ea98aaef1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019eb280-b211-7e2f-b29a-fb0476cd0eb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019eb280-b211-7383-8217-a94ea98aaef1" xlink:to="loc_us-gaap_SalesRevenueNetMember_019eb280-b211-7e2f-b29a-fb0476cd0eb8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019eb280-b211-7cfb-82c4-00fd30391b3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019eb280-b211-7301-ab96-ec37018ba7e3" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019eb280-b211-7cfb-82c4-00fd30391b3a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019eb280-b211-7cfb-82c4-00fd30391b3a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019eb280-b211-7cfb-82c4-00fd30391b3a" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019eb280-b211-7cfb-82c4-00fd30391b3a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019eb280-b211-7274-a97d-eb582ffbc475" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019eb280-b211-7cfb-82c4-00fd30391b3a" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019eb280-b211-7274-a97d-eb582ffbc475" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_019eb280-b211-7ca1-aef2-16f68b5b0348" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019eb280-b211-7274-a97d-eb582ffbc475" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_019eb280-b211-7ca1-aef2-16f68b5b0348" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019eb280-b211-7fae-8e7a-7fa1898c3ce2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019eb280-b211-7ef2-b662-8ebb70b30863" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019eb280-b211-7fae-8e7a-7fa1898c3ce2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019eb280-b211-7900-8a19-65ec58af668e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019eb280-b211-7ef2-b662-8ebb70b30863" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019eb280-b211-7900-8a19-65ec58af668e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/CASHEQUIVALENTSANDMARKETABLESECURITIESDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#CASHEQUIVALENTSANDMARKETABLESECURITIESDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/CASHEQUIVALENTSANDMARKETABLESECURITIESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019eb280-b211-7abc-9b2a-92a5d2a80695" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019eb280-b211-7222-baf4-9549919f7be2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019eb280-b211-7abc-9b2a-92a5d2a80695" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019eb280-b211-7222-baf4-9549919f7be2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019fb49e-a607-7c89-bad0-7c15708e0be9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019eb280-b211-7222-baf4-9549919f7be2" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019fb49e-a607-7c89-bad0-7c15708e0be9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fb49e-a607-7c89-bad0-7c15708e0be9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019fb49e-a607-7c89-bad0-7c15708e0be9" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fb49e-a607-7c89-bad0-7c15708e0be9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fb49e-a607-70ce-b5c7-9422660764bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019fb49e-a607-7c89-bad0-7c15708e0be9" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fb49e-a607-70ce-b5c7-9422660764bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019eb280-b211-795a-b646-cfc871f8e822" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019fb49e-a607-70ce-b5c7-9422660764bf" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019eb280-b211-795a-b646-cfc871f8e822" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019eb280-b211-791c-a485-f66737b01914" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019eb280-b211-7222-baf4-9549919f7be2" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019eb280-b211-791c-a485-f66737b01914" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eb280-b211-791c-a485-f66737b01914_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019eb280-b211-791c-a485-f66737b01914" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eb280-b211-791c-a485-f66737b01914_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eb280-b211-75b7-a0b0-cee31716f5fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019eb280-b211-791c-a485-f66737b01914" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eb280-b211-75b7-a0b0-cee31716f5fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember_019eb280-b211-7a4e-9103-299c92e44895" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019eb280-b211-75b7-a0b0-cee31716f5fe" xlink:to="loc_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember_019eb280-b211-7a4e-9103-299c92e44895" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019fb49e-5253-7a42-a4c8-e8935ccda728" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019eb280-b211-7abc-9b2a-92a5d2a80695" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019fb49e-5253-7a42-a4c8-e8935ccda728" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019eb280-b211-7720-b5f3-1c4541b66182" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019eb280-b211-7abc-9b2a-92a5d2a80695" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019eb280-b211-7720-b5f3-1c4541b66182" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_CashCashEquivalentsAndShortTermInvestmentsAmortizedCost_019fb4a2-cb16-7984-b12b-a4c5495ef5fd" xlink:href="irtc-20260630.xsd#irtc_CashCashEquivalentsAndShortTermInvestmentsAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019eb280-b211-7abc-9b2a-92a5d2a80695" xlink:to="loc_irtc_CashCashEquivalentsAndShortTermInvestmentsAmortizedCost_019fb4a2-cb16-7984-b12b-a4c5495ef5fd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019eb280-b211-7d2a-8a57-ad697171090c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019eb280-b211-7abc-9b2a-92a5d2a80695" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019eb280-b211-7d2a-8a57-ad697171090c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019eb280-b211-7302-a467-355947ad6023" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019eb280-b211-7abc-9b2a-92a5d2a80695" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019eb280-b211-7302-a467-355947ad6023" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashEquivalentsAtCarryingValue_019eb280-b211-7ed6-bb2f-6d304e339ebd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019eb280-b211-7abc-9b2a-92a5d2a80695" xlink:to="loc_us-gaap_CashEquivalentsAtCarryingValue_019eb280-b211-7ed6-bb2f-6d304e339ebd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019eb280-b211-7021-a81f-4bce096e409e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019eb280-b211-7abc-9b2a-92a5d2a80695" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019eb280-b211-7021-a81f-4bce096e409e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsAndShortTermInvestments_019eb280-b211-7dd2-9ed1-16a25086e18b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsAndShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019eb280-b211-7abc-9b2a-92a5d2a80695" xlink:to="loc_us-gaap_CashCashEquivalentsAndShortTermInvestments_019eb280-b211-7dd2-9ed1-16a25086e18b" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSScheduleofFairValueofCompanysFinancialAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#FAIRVALUEMEASUREMENTSScheduleofFairValueofCompanysFinancialAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSScheduleofFairValueofCompanysFinancialAssetsandLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-77c5-91b3-3f09f07ba7f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-732e-b997-9468ae9de344" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-77c5-91b3-3f09f07ba7f1" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-732e-b997-9468ae9de344" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7d95-8cd6-f398dd1e22a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-732e-b997-9468ae9de344" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7d95-8cd6-f398dd1e22a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7d95-8cd6-f398dd1e22a4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7d95-8cd6-f398dd1e22a4" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7d95-8cd6-f398dd1e22a4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-733b-95cb-23b8fc8a9750" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7d95-8cd6-f398dd1e22a4" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-733b-95cb-23b8fc8a9750" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019eb280-b211-773a-8542-941a4c8f9860" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-733b-95cb-23b8fc8a9750" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019eb280-b211-773a-8542-941a4c8f9860" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019eb280-b211-753d-a2ff-0d3c80bf09f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-733b-95cb-23b8fc8a9750" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019eb280-b211-753d-a2ff-0d3c80bf09f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019eb280-b211-7a77-a020-23c035c56211" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-733b-95cb-23b8fc8a9750" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019eb280-b211-7a77-a020-23c035c56211" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019f8169-c112-7ddc-99ae-9bdad99ad68d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-77c5-91b3-3f09f07ba7f1" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019f8169-c112-7ddc-99ae-9bdad99ad68d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019f816a-8b12-75e4-a9d5-ed7f2eb8aacb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-77c5-91b3-3f09f07ba7f1" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019f816a-8b12-75e4-a9d5-ed7f2eb8aacb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AlternativeInvestment_019f816b-a811-71f0-8049-cbe73c482081" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AlternativeInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-77c5-91b3-3f09f07ba7f1" xlink:to="loc_us-gaap_AlternativeInvestment_019f816b-a811-71f0-8049-cbe73c482081" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019eb280-b211-7707-9bdc-ca044f3d4c7f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-77c5-91b3-3f09f07ba7f1" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019eb280-b211-7707-9bdc-ca044f3d4c7f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionContingentConsiderationLiability_019f816c-de34-73fd-b86a-39fe29817cd9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-77c5-91b3-3f09f07ba7f1" xlink:to="loc_us-gaap_AssetAcquisitionContingentConsiderationLiability_019f816c-de34-73fd-b86a-39fe29817cd9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019eb280-b211-76e4-a93f-60aeef6be538" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-77c5-91b3-3f09f07ba7f1" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019eb280-b211-76e4-a93f-60aeef6be538" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSScheduleofChangesinEstimatedFairValueofStrategicInvestmentsMeasuredonRecurringBasisDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#FAIRVALUEMEASUREMENTSScheduleofChangesinEstimatedFairValueofStrategicInvestmentsMeasuredonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSScheduleofChangesinEstimatedFairValueofStrategicInvestmentsMeasuredonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7aa1-8d98-7a184a61f951" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7751-926c-58996726cd5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7aa1-8d98-7a184a61f951" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7751-926c-58996726cd5e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7e5e-a4b1-2f096bc099dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7751-926c-58996726cd5e" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7e5e-a4b1-2f096bc099dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7e5e-a4b1-2f096bc099dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7e5e-a4b1-2f096bc099dc" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7e5e-a4b1-2f096bc099dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7fb9-9308-7f2eb36dd5c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7e5e-a4b1-2f096bc099dc" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7fb9-9308-7f2eb36dd5c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019eb280-b211-72ec-88e6-475f67111577" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7fb9-9308-7f2eb36dd5c4" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019eb280-b211-72ec-88e6-475f67111577" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_ChangeInFairValueOfStrategicInvestmentsRollForward_019eb280-b211-7473-96b8-0f1aa18749f9" xlink:href="irtc-20260630.xsd#irtc_ChangeInFairValueOfStrategicInvestmentsRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7aa1-8d98-7a184a61f951" xlink:to="loc_irtc_ChangeInFairValueOfStrategicInvestmentsRollForward_019eb280-b211-7473-96b8-0f1aa18749f9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_StrategicInvestments_019eb280-b211-73a3-8481-69dcdb77025b" xlink:href="irtc-20260630.xsd#irtc_StrategicInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_irtc_ChangeInFairValueOfStrategicInvestmentsRollForward_019eb280-b211-7473-96b8-0f1aa18749f9" xlink:to="loc_irtc_StrategicInvestments_019eb280-b211-73a3-8481-69dcdb77025b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_StrategicInvestmentAdditions_019eb280-b211-7fbe-b58c-004aded5f845" xlink:href="irtc-20260630.xsd#irtc_StrategicInvestmentAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_irtc_ChangeInFairValueOfStrategicInvestmentsRollForward_019eb280-b211-7473-96b8-0f1aa18749f9" xlink:to="loc_irtc_StrategicInvestmentAdditions_019eb280-b211-7fbe-b58c-004aded5f845" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_StrategicInvestmentChangesInFairValue_019eb280-b211-762d-b55a-7b196eb298c2" xlink:href="irtc-20260630.xsd#irtc_StrategicInvestmentChangesInFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_irtc_ChangeInFairValueOfStrategicInvestmentsRollForward_019eb280-b211-7473-96b8-0f1aa18749f9" xlink:to="loc_irtc_StrategicInvestmentChangesInFairValue_019eb280-b211-762d-b55a-7b196eb298c2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_StrategicInvestments_019eb280-b211-7e0e-8a1f-ce97fd85889d" xlink:href="irtc-20260630.xsd#irtc_StrategicInvestments"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSNarrativeDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#FAIRVALUEMEASUREMENTSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7cd7-82ac-8e36ce7a404a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7898-b3a6-e16ce3b2c8aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7cd7-82ac-8e36ce7a404a" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7898-b3a6-e16ce3b2c8aa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019ef8cf-3f19-77c4-88c3-6f8535e4f756" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7898-b3a6-e16ce3b2c8aa" xlink:to="loc_dei_LegalEntityAxis_019ef8cf-3f19-77c4-88c3-6f8535e4f756" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019ef8cf-3f19-77c4-88c3-6f8535e4f756_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019ef8cf-3f19-77c4-88c3-6f8535e4f756" xlink:to="loc_dei_EntityDomain_019ef8cf-3f19-77c4-88c3-6f8535e4f756_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019ef8cf-3f19-70bb-a8c1-9bcccd695815" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019ef8cf-3f19-77c4-88c3-6f8535e4f756" xlink:to="loc_dei_EntityDomain_019ef8cf-3f19-70bb-a8c1-9bcccd695815" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_BioIntelliSenseInc.Member_019ef8cf-3f19-78b5-9927-7b60e399620f" xlink:href="irtc-20260630.xsd#irtc_BioIntelliSenseInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019ef8cf-3f19-70bb-a8c1-9bcccd695815" xlink:to="loc_irtc_BioIntelliSenseInc.Member_019ef8cf-3f19-78b5-9927-7b60e399620f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ef8cf-3f19-7e9f-9655-c70ccfab0ff6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7898-b3a6-e16ce3b2c8aa" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ef8cf-3f19-7e9f-9655-c70ccfab0ff6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ef8cf-3f19-7e9f-9655-c70ccfab0ff6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ef8cf-3f19-7e9f-9655-c70ccfab0ff6" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ef8cf-3f19-7e9f-9655-c70ccfab0ff6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ef8cf-3f19-77f1-8544-8fdee8648bb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ef8cf-3f19-7e9f-9655-c70ccfab0ff6" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ef8cf-3f19-77f1-8544-8fdee8648bb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019ef8cf-3f19-7748-9f34-5e94bacc4abe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ef8cf-3f19-77f1-8544-8fdee8648bb9" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019ef8cf-3f19-7748-9f34-5e94bacc4abe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_IncreaseDecreaseInFairValueOfStrategicLoanInvestments_019f6cb8-70e0-7382-8ea4-a9988192226e" xlink:href="irtc-20260630.xsd#irtc_IncreaseDecreaseInFairValueOfStrategicLoanInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7cd7-82ac-8e36ce7a404a" xlink:to="loc_irtc_IncreaseDecreaseInFairValueOfStrategicLoanInvestments_019f6cb8-70e0-7382-8ea4-a9988192226e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_FairValueOfStrategicLoanInvestment_019ef8ce-e45c-7e21-8b5d-1020b1897771" xlink:href="irtc-20260630.xsd#irtc_FairValueOfStrategicLoanInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7cd7-82ac-8e36ce7a404a" xlink:to="loc_irtc_FairValueOfStrategicLoanInvestment_019ef8ce-e45c-7e21-8b5d-1020b1897771" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_IncreaseDecreaseInFairValueOfStrategicEquityInvestments_019f6cc3-e5bc-712b-aeba-ffec5e693e30" xlink:href="irtc-20260630.xsd#irtc_IncreaseDecreaseInFairValueOfStrategicEquityInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7cd7-82ac-8e36ce7a404a" xlink:to="loc_irtc_IncreaseDecreaseInFairValueOfStrategicEquityInvestments_019f6cc3-e5bc-712b-aeba-ffec5e693e30" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionContingentConsiderationLiability_019ef8cf-3f19-73c0-9bbc-b89d34e457a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7cd7-82ac-8e36ce7a404a" xlink:to="loc_us-gaap_AssetAcquisitionContingentConsiderationLiability_019ef8cf-3f19-73c0-9bbc-b89d34e457a8" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSScheduleofTheRecurringLevel3FairValueMeasurementsofTheLoanInvestmentDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#FAIRVALUEMEASUREMENTSScheduleofTheRecurringLevel3FairValueMeasurementsofTheLoanInvestmentDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSScheduleofTheRecurringLevel3FairValueMeasurementsofTheLoanInvestmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7742-acca-78a4b40e7126" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-767a-9abc-a92e18b65a25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7742-acca-78a4b40e7126" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-767a-9abc-a92e18b65a25" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7966-aec4-8bee9d53344a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-767a-9abc-a92e18b65a25" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7966-aec4-8bee9d53344a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7966-aec4-8bee9d53344a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7966-aec4-8bee9d53344a" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7966-aec4-8bee9d53344a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7554-91e4-044f2226afd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7966-aec4-8bee9d53344a" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7554-91e4-044f2226afd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019eb280-b211-7af1-91b0-e9b6bf72acab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7554-91e4-044f2226afd2" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019eb280-b211-7af1-91b0-e9b6bf72acab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019eb280-b211-737d-a81c-724e8ec18f95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-767a-9abc-a92e18b65a25" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019eb280-b211-737d-a81c-724e8ec18f95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019eb280-b211-737d-a81c-724e8ec18f95_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019eb280-b211-737d-a81c-724e8ec18f95" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019eb280-b211-737d-a81c-724e8ec18f95_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019eb280-b211-71b0-9eea-5569ebd73fd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019eb280-b211-737d-a81c-724e8ec18f95" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019eb280-b211-71b0-9eea-5569ebd73fd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019eb280-b211-7ef9-a3c7-9fd4a0049079" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019eb280-b211-71b0-9eea-5569ebd73fd2" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019eb280-b211-7ef9-a3c7-9fd4a0049079" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019eb280-b211-7b22-a4a1-95b4c7699508" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-767a-9abc-a92e18b65a25" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019eb280-b211-7b22-a4a1-95b4c7699508" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-7b22-a4a1-95b4c7699508_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019eb280-b211-7b22-a4a1-95b4c7699508" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-7b22-a4a1-95b4c7699508_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-7942-a932-f5267be1b532" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019eb280-b211-7b22-a4a1-95b4c7699508" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-7942-a932-f5267be1b532" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_019eb280-b211-757d-ac1c-26359e019948" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-7942-a932-f5267be1b532" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_019eb280-b211-757d-ac1c-26359e019948" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputOptionVolatilityMember_019eb280-b211-7b25-9990-d2125f6846c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputOptionVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-7942-a932-f5267be1b532" xlink:to="loc_us-gaap_MeasurementInputOptionVolatilityMember_019eb280-b211-7b25-9990-d2125f6846c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_019eb280-b211-7b9c-8dc9-2cae9e85af29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-7942-a932-f5267be1b532" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_019eb280-b211-7b9c-8dc9-2cae9e85af29" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_LoanInvestmentMeasurementInput_019eb280-b211-71f8-90b3-7db868b7f632" xlink:href="irtc-20260630.xsd#irtc_LoanInvestmentMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7742-acca-78a4b40e7126" xlink:to="loc_irtc_LoanInvestmentMeasurementInput_019eb280-b211-71f8-90b3-7db868b7f632" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_LoanInvestmentTerm_019eb280-b211-7cde-866d-7f6f5b0a1a18" xlink:href="irtc-20260630.xsd#irtc_LoanInvestmentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7742-acca-78a4b40e7126" xlink:to="loc_irtc_LoanInvestmentTerm_019eb280-b211-7cde-866d-7f6f5b0a1a18" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSScheduleofTheRecurringLevel3FairValueMeasurementsofContingentConsiderationLiabilitiesDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#FAIRVALUEMEASUREMENTSScheduleofTheRecurringLevel3FairValueMeasurementsofContingentConsiderationLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSScheduleofTheRecurringLevel3FairValueMeasurementsofContingentConsiderationLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7d71-9b9c-c2688a816afd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7b77-bb55-8376cea8ccf2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7d71-9b9c-c2688a816afd" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7b77-bb55-8376cea8ccf2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7bdc-9c3d-ec71b4e3373c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7b77-bb55-8376cea8ccf2" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7bdc-9c3d-ec71b4e3373c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7bdc-9c3d-ec71b4e3373c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7bdc-9c3d-ec71b4e3373c" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7bdc-9c3d-ec71b4e3373c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-76f0-b197-394057864648" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7bdc-9c3d-ec71b4e3373c" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-76f0-b197-394057864648" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019eb280-b211-7b2e-981c-6ef71888fa85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-76f0-b197-394057864648" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019eb280-b211-7b2e-981c-6ef71888fa85" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019eb280-b211-7043-95d1-02b598d2952e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7b77-bb55-8376cea8ccf2" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019eb280-b211-7043-95d1-02b598d2952e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019eb280-b211-7043-95d1-02b598d2952e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019eb280-b211-7043-95d1-02b598d2952e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019eb280-b211-7043-95d1-02b598d2952e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019eb280-b211-722a-b592-2031e57cbdfb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019eb280-b211-7043-95d1-02b598d2952e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019eb280-b211-722a-b592-2031e57cbdfb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019eb280-b211-786e-8e38-67d76172de43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019eb280-b211-722a-b592-2031e57cbdfb" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019eb280-b211-786e-8e38-67d76172de43" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019eb280-b211-77e9-94a4-85e39ef72713" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7b77-bb55-8376cea8ccf2" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019eb280-b211-77e9-94a4-85e39ef72713" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-77e9-94a4-85e39ef72713_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019eb280-b211-77e9-94a4-85e39ef72713" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-77e9-94a4-85e39ef72713_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-7244-a3e0-498c2967f0f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019eb280-b211-77e9-94a4-85e39ef72713" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-7244-a3e0-498c2967f0f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_MeasurementInputProbabilityOfLoanForgivenessMember_019eb280-b211-7295-ba5a-77b519cf27b9" xlink:href="irtc-20260630.xsd#irtc_MeasurementInputProbabilityOfLoanForgivenessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-7244-a3e0-498c2967f0f2" xlink:to="loc_irtc_MeasurementInputProbabilityOfLoanForgivenessMember_019eb280-b211-7295-ba5a-77b519cf27b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_019eb280-b211-752a-8f74-b13f95b689ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019eb280-b211-7244-a3e0-498c2967f0f2" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_019eb280-b211-752a-8f74-b13f95b689ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019eb280-b211-7a43-99fd-1f4f23ad55eb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7b77-bb55-8376cea8ccf2" xlink:to="loc_srt_RangeAxis_019eb280-b211-7a43-99fd-1f4f23ad55eb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eb280-b211-7a43-99fd-1f4f23ad55eb_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019eb280-b211-7a43-99fd-1f4f23ad55eb" xlink:to="loc_srt_RangeMember_019eb280-b211-7a43-99fd-1f4f23ad55eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eb280-b211-79b7-9707-5079fab7f4fc" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019eb280-b211-7a43-99fd-1f4f23ad55eb" xlink:to="loc_srt_RangeMember_019eb280-b211-79b7-9707-5079fab7f4fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019eb280-b211-7edc-a42a-514b2ce65a9c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eb280-b211-79b7-9707-5079fab7f4fc" xlink:to="loc_srt_MinimumMember_019eb280-b211-7edc-a42a-514b2ce65a9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019eb280-b211-7a87-ac8a-7f738e395bce" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eb280-b211-79b7-9707-5079fab7f4fc" xlink:to="loc_srt_MaximumMember_019eb280-b211-7a87-ac8a-7f738e395bce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_ContingentConsiderationMeasurementInput_019eb280-b211-7f6c-9b37-03cab5a2e30c" xlink:href="irtc-20260630.xsd#irtc_ContingentConsiderationMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7d71-9b9c-c2688a816afd" xlink:to="loc_irtc_ContingentConsiderationMeasurementInput_019eb280-b211-7f6c-9b37-03cab5a2e30c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_ContingentConsiderationTerm_019eb280-b211-77f7-aa28-af398ff0c857" xlink:href="irtc-20260630.xsd#irtc_ContingentConsiderationTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7d71-9b9c-c2688a816afd" xlink:to="loc_irtc_ContingentConsiderationTerm_019eb280-b211-77f7-aa28-af398ff0c857" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSScheduleofChangesinEstimatedFairValueofContingentConsiderationLiabilitiesMeasuredonaRecurringBasisLevel3Details" xlink:type="simple" xlink:href="irtc-20260630.xsd#FAIRVALUEMEASUREMENTSScheduleofChangesinEstimatedFairValueofContingentConsiderationLiabilitiesMeasuredonaRecurringBasisLevel3Details"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSScheduleofChangesinEstimatedFairValueofContingentConsiderationLiabilitiesMeasuredonaRecurringBasisLevel3Details" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7a71-b15d-f308520592a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7366-b02d-cc3ae807b795" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7a71-b15d-f308520592a8" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7366-b02d-cc3ae807b795" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7ff0-87bd-ad14fa9f1838" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-7366-b02d-cc3ae807b795" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7ff0-87bd-ad14fa9f1838" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7ff0-87bd-ad14fa9f1838_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7ff0-87bd-ad14fa9f1838" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-7ff0-87bd-ad14fa9f1838_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-753c-af0f-87b59fb1bd0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019eb280-b211-7ff0-87bd-ad14fa9f1838" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-753c-af0f-87b59fb1bd0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019eb280-b211-74b0-9de0-13a2dd3459aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019eb280-b211-753c-af0f-87b59fb1bd0c" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019eb280-b211-74b0-9de0-13a2dd3459aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019eb280-b211-7f61-95a1-79653dc9d142" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7a71-b15d-f308520592a8" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019eb280-b211-7f61-95a1-79653dc9d142" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019eb280-b211-7644-8e86-5eb5d835c268" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019eb280-b211-7f61-95a1-79653dc9d142" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019eb280-b211-7644-8e86-5eb5d835c268" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAdditions_019eb280-b211-7009-b151-726521b23fa3" xlink:href="irtc-20260630.xsd#irtc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019eb280-b211-7f61-95a1-79653dc9d142" xlink:to="loc_irtc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAdditions_019eb280-b211-7009-b151-726521b23fa3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019eb280-b211-778a-afc8-ac45bf7d2f15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019eb280-b211-7f61-95a1-79653dc9d142" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019eb280-b211-778a-afc8-ac45bf7d2f15" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019eb280-b211-7231-9c6d-f876e5a3dcb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSScheduleofFairValueofSeniorConvertibleNotesDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#FAIRVALUEMEASUREMENTSScheduleofFairValueofSeniorConvertibleNotesDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/FAIRVALUEMEASUREMENTSScheduleofFairValueofSeniorConvertibleNotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7364-8ab8-577aeeff5d8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-78f5-b810-e1744fe28735" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7364-8ab8-577aeeff5d8a" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-78f5-b810-e1744fe28735" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-7143-a444-e118ec40e69a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-78f5-b810-e1744fe28735" xlink:to="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-7143-a444-e118ec40e69a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-7143-a444-e118ec40e69a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-7143-a444-e118ec40e69a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-7143-a444-e118ec40e69a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-7812-a132-56ec2af4a2e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-7143-a444-e118ec40e69a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-7812-a132-56ec2af4a2e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_ConvertibleNotesDue2029Member_019eb280-b211-76e1-ac3b-0d8a97f24743" xlink:href="irtc-20260630.xsd#irtc_ConvertibleNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-7812-a132-56ec2af4a2e5" xlink:to="loc_irtc_ConvertibleNotesDue2029Member_019eb280-b211-76e1-ac3b-0d8a97f24743" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-7c87-baeb-8b962feb805c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019eb280-b211-78f5-b810-e1744fe28735" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-7c87-baeb-8b962feb805c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7c87-baeb-8b962feb805c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-7c87-baeb-8b962feb805c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7c87-baeb-8b962feb805c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7168-9b40-e226dead732e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-7c87-baeb-8b962feb805c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7168-9b40-e226dead732e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019eb280-b211-74fd-a60d-a76d60830719" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7168-9b40-e226dead732e" xlink:to="loc_us-gaap_SeniorNotesMember_019eb280-b211-74fd-a60d-a76d60830719" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtFairValueDisclosures_019eb280-b211-7c5e-9cda-da6d577d36dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtFairValueDisclosures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019eb280-b211-7364-8ab8-577aeeff5d8a" xlink:to="loc_us-gaap_ConvertibleDebtFairValueDisclosures_019eb280-b211-7c5e-9cda-da6d577d36dd" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/BALANCESHEETCOMPONENTSNarrativeDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#BALANCESHEETCOMPONENTSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/BALANCESHEETCOMPONENTSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryLineItems_019eb280-b211-7b8b-a8b9-16db5ad7347c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryCurrentTable_019eb280-b211-74c2-b301-7d750455a7c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryCurrentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_InventoryLineItems_019eb280-b211-7b8b-a8b9-16db5ad7347c" xlink:to="loc_us-gaap_InventoryCurrentTable_019eb280-b211-74c2-b301-7d750455a7c1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesInventoryAxis_019eb280-b211-732f-8bec-204c4aeb1ea9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesInventoryAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InventoryCurrentTable_019eb280-b211-74c2-b301-7d750455a7c1" xlink:to="loc_us-gaap_PublicUtilitiesInventoryAxis_019eb280-b211-732f-8bec-204c4aeb1ea9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_019eb280-b211-732f-8bec-204c4aeb1ea9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PublicUtilitiesInventoryAxis_019eb280-b211-732f-8bec-204c4aeb1ea9" xlink:to="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_019eb280-b211-732f-8bec-204c4aeb1ea9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_019eb280-b211-78b1-b0fd-b1c58c6ee064" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PublicUtilitiesInventoryAxis_019eb280-b211-732f-8bec-204c4aeb1ea9" xlink:to="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_019eb280-b211-78b1-b0fd-b1c58c6ee064" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_PrintedCircuitBoardAssembliesMember_019eb280-b211-7fe7-a3ac-e1fcfa026a68" xlink:href="irtc-20260630.xsd#irtc_PrintedCircuitBoardAssembliesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_019eb280-b211-78b1-b0fd-b1c58c6ee064" xlink:to="loc_irtc_PrintedCircuitBoardAssembliesMember_019eb280-b211-7fe7-a3ac-e1fcfa026a68" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eb280-b211-7050-b328-03ddf78e5f19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InventoryCurrentTable_019eb280-b211-74c2-b301-7d750455a7c1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eb280-b211-7050-b328-03ddf78e5f19" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7050-b328-03ddf78e5f19_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eb280-b211-7050-b328-03ddf78e5f19" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7050-b328-03ddf78e5f19_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7098-86e0-d78d24097dc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eb280-b211-7050-b328-03ddf78e5f19" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7098-86e0-d78d24097dc3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_019eb280-b211-780c-b4c4-f0809d5cba27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7098-86e0-d78d24097dc3" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_019eb280-b211-780c-b4c4-f0809d5cba27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_019eb280-b211-73a9-a865-8b26d7592d58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_019eb280-b211-7b8b-a8b9-16db5ad7347c" xlink:to="loc_us-gaap_CostOfRevenue_019eb280-b211-73a9-a865-8b26d7592d58" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_AssetsPurchaseAccountingAdjustmentsOtherAssetsPCBAs_019eb280-b211-7860-a0f5-8708bf394e39" xlink:href="irtc-20260630.xsd#irtc_AssetsPurchaseAccountingAdjustmentsOtherAssetsPCBAs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_019eb280-b211-7b8b-a8b9-16db5ad7347c" xlink:to="loc_irtc_AssetsPurchaseAccountingAdjustmentsOtherAssetsPCBAs_019eb280-b211-7860-a0f5-8708bf394e39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentForAmortization_019eb280-b211-742c-9a56-6730901cde25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentForAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_019eb280-b211-7b8b-a8b9-16db5ad7347c" xlink:to="loc_us-gaap_AdjustmentForAmortization_019eb280-b211-742c-9a56-6730901cde25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019eb280-b211-72cb-a21e-7dac61347e1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_019eb280-b211-7b8b-a8b9-16db5ad7347c" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019eb280-b211-72cb-a21e-7dac61347e1d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedComputerSoftwareAdditions_019eb280-b211-758e-942e-a1c84addf15c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalizedComputerSoftwareAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_019eb280-b211-7b8b-a8b9-16db5ad7347c" xlink:to="loc_us-gaap_CapitalizedComputerSoftwareAdditions_019eb280-b211-758e-942e-a1c84addf15c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_019ed54d-c740-75b4-9031-4eb340ae7d0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_019eb280-b211-7b8b-a8b9-16db5ad7347c" xlink:to="loc_us-gaap_AssetImpairmentCharges_019ed54d-c740-75b4-9031-4eb340ae7d0d" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/BALANCESHEETCOMPONENTSScheduleofPropertyandEquipmentNetDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#BALANCESHEETCOMPONENTSScheduleofPropertyandEquipmentNetDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/BALANCESHEETCOMPONENTSScheduleofPropertyandEquipmentNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019eb280-b211-7e79-a6cf-c6f5beb70368" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019eb280-b211-78b6-8352-10194cfc654c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019eb280-b211-7e79-a6cf-c6f5beb70368" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019eb280-b211-78b6-8352-10194cfc654c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eb280-b211-77d5-8d60-d90e6d873ded" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019eb280-b211-78b6-8352-10194cfc654c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eb280-b211-77d5-8d60-d90e6d873ded" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-77d5-8d60-d90e6d873ded_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eb280-b211-77d5-8d60-d90e6d873ded" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-77d5-8d60-d90e6d873ded_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7ac3-a4be-caaeb9040403" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019eb280-b211-77d5-8d60-d90e6d873ded" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7ac3-a4be-caaeb9040403" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_LaboratoryAndManufacturingEquipmentMember_019eb280-b211-775d-8003-d340d56ef819" xlink:href="irtc-20260630.xsd#irtc_LaboratoryAndManufacturingEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7ac3-a4be-caaeb9040403" xlink:to="loc_irtc_LaboratoryAndManufacturingEquipmentMember_019eb280-b211-775d-8003-d340d56ef819" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_ComputerEquipmentAndSoftwareMember_019eb280-b211-7c98-a0a0-5ff4ea3009fd" xlink:href="irtc-20260630.xsd#irtc_ComputerEquipmentAndSoftwareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7ac3-a4be-caaeb9040403" xlink:to="loc_irtc_ComputerEquipmentAndSoftwareMember_019eb280-b211-7c98-a0a0-5ff4ea3009fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_019eb280-b211-70af-830c-9fd4e7dc4880" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7ac3-a4be-caaeb9040403" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_019eb280-b211-70af-830c-9fd4e7dc4880" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019eb280-b211-7d26-8457-d005f901deba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7ac3-a4be-caaeb9040403" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019eb280-b211-7d26-8457-d005f901deba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_019eb280-b211-7eee-af1c-a15b614a9812" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7ac3-a4be-caaeb9040403" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_019eb280-b211-7eee-af1c-a15b614a9812" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareInDevelopmentMember_019eb280-b211-726c-b901-dd87f3391a25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareInDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7ac3-a4be-caaeb9040403" xlink:to="loc_us-gaap_SoftwareInDevelopmentMember_019eb280-b211-726c-b901-dd87f3391a25" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_019eb280-b211-7936-beda-fbccd2aaa804" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019eb280-b211-7ac3-a4be-caaeb9040403" xlink:to="loc_us-gaap_ConstructionInProgressMember_019eb280-b211-7936-beda-fbccd2aaa804" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019eb280-b211-7c5a-8908-6dacbf4c9008" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019eb280-b211-78b6-8352-10194cfc654c" xlink:to="loc_srt_RangeAxis_019eb280-b211-7c5a-8908-6dacbf4c9008" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eb280-b211-7c5a-8908-6dacbf4c9008_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019eb280-b211-7c5a-8908-6dacbf4c9008" xlink:to="loc_srt_RangeMember_019eb280-b211-7c5a-8908-6dacbf4c9008_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eb280-b211-793f-85ba-6b2df0da9b84" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019eb280-b211-7c5a-8908-6dacbf4c9008" xlink:to="loc_srt_RangeMember_019eb280-b211-793f-85ba-6b2df0da9b84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019eb280-b211-7dd3-a6d2-a4eb075dfe27" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eb280-b211-793f-85ba-6b2df0da9b84" xlink:to="loc_srt_MinimumMember_019eb280-b211-7dd3-a6d2-a4eb075dfe27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019eb280-b211-7522-addc-0a241c769f9a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eb280-b211-793f-85ba-6b2df0da9b84" xlink:to="loc_srt_MaximumMember_019eb280-b211-7522-addc-0a241c769f9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019eb280-b211-7363-8c7f-9f086c821098" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019eb280-b211-7e79-a6cf-c6f5beb70368" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019eb280-b211-7363-8c7f-9f086c821098" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019eb280-b211-7ef5-9f69-eb86b828c3d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019eb280-b211-7e79-a6cf-c6f5beb70368" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019eb280-b211-7ef5-9f69-eb86b828c3d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019eb280-b211-7455-a630-96811f372858" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019eb280-b211-7e79-a6cf-c6f5beb70368" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019eb280-b211-7455-a630-96811f372858" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019eb280-b211-7e99-9146-c8419476f0f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019eb280-b211-7e79-a6cf-c6f5beb70368" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019eb280-b211-7e99-9146-c8419476f0f6" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/COMMITMENTSANDCONTINGENCIESNarrativeDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#COMMITMENTSANDCONTINGENCIESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/COMMITMENTSANDCONTINGENCIESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019f44ea-1ff2-752e-8495-62ce723da586" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfFinancialPositionLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019f44ea-1ff2-752e-8495-62ce723da586" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseAxis_019f6cb0-a029-7818-9d73-c7e2205282f7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:to="loc_srt_LitigationCaseAxis_019f6cb0-a029-7818-9d73-c7e2205282f7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019f6cb0-a029-7818-9d73-c7e2205282f7_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_LitigationCaseAxis_019f6cb0-a029-7818-9d73-c7e2205282f7" xlink:to="loc_srt_LitigationCaseTypeDomain_019f6cb0-a029-7818-9d73-c7e2205282f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019f6cb0-d9bd-792e-97d2-7418516918c3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_LitigationCaseAxis_019f6cb0-a029-7818-9d73-c7e2205282f7" xlink:to="loc_srt_LitigationCaseTypeDomain_019f6cb0-d9bd-792e-97d2-7418516918c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_ClassActionMember_019f6cb2-2359-72df-a0ac-372b91b5278e" xlink:href="irtc-20260630.xsd#irtc_ClassActionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_LitigationCaseTypeDomain_019f6cb0-d9bd-792e-97d2-7418516918c3" xlink:to="loc_irtc_ClassActionMember_019f6cb2-2359-72df-a0ac-372b91b5278e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_019f44ea-6b59-7a76-9271-a801f96706f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_019f44ea-6b59-7a76-9271-a801f96706f2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019f44ea-6b59-7a76-9271-a801f96706f2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019f44ea-6b59-7a76-9271-a801f96706f2" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019f44ea-6b59-7a76-9271-a801f96706f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019f44ea-6b59-7614-9b32-29243d6731ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019f44ea-6b59-7a76-9271-a801f96706f2" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019f44ea-6b59-7614-9b32-29243d6731ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleNotesPayableMember_019f44ea-6b59-77c9-b016-075c19905207" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleNotesPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019f44ea-6b59-7614-9b32-29243d6731ec" xlink:to="loc_us-gaap_ConvertibleNotesPayableMember_019f44ea-6b59-77c9-b016-075c19905207" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_MilestoneNotesMember_019f44ea-6b59-70a3-90c0-9aac9b7c050f" xlink:href="irtc-20260630.xsd#irtc_MilestoneNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019f44ea-6b59-7614-9b32-29243d6731ec" xlink:to="loc_irtc_MilestoneNotesMember_019f44ea-6b59-70a3-90c0-9aac9b7c050f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019f44ea-6b59-79ec-aa95-cc1498e1d482" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:to="loc_dei_LegalEntityAxis_019f44ea-6b59-79ec-aa95-cc1498e1d482" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019f44ea-6b59-79ec-aa95-cc1498e1d482_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019f44ea-6b59-79ec-aa95-cc1498e1d482" xlink:to="loc_dei_EntityDomain_019f44ea-6b59-79ec-aa95-cc1498e1d482_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019f44ea-6b59-7791-afd5-87dd4235df81" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019f44ea-6b59-79ec-aa95-cc1498e1d482" xlink:to="loc_dei_EntityDomain_019f44ea-6b59-7791-afd5-87dd4235df81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_BioIntelliSenseInc.Member_019f44ea-6b59-7046-b832-78ce4080fad0" xlink:href="irtc-20260630.xsd#irtc_BioIntelliSenseInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019f44ea-6b59-7791-afd5-87dd4235df81" xlink:to="loc_irtc_BioIntelliSenseInc.Member_019f44ea-6b59-7046-b832-78ce4080fad0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f44ea-6b59-7d2a-8b32-03b98baa4374" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f44ea-6b59-7d2a-8b32-03b98baa4374" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f44ea-6b59-7d2a-8b32-03b98baa4374_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f44ea-6b59-7d2a-8b32-03b98baa4374" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f44ea-6b59-7d2a-8b32-03b98baa4374_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f44ea-6b59-7ac5-87c9-32c0499e0180" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f44ea-6b59-7d2a-8b32-03b98baa4374" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f44ea-6b59-7ac5-87c9-32c0499e0180" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_019f44ea-6b59-7185-ac4a-d9399094335a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f44ea-6b59-7ac5-87c9-32c0499e0180" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_019f44ea-6b59-7185-ac4a-d9399094335a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_AccruedHealthBenefitsLiability_019f44ea-1ff2-7bea-9802-bb4560a5f067" xlink:href="irtc-20260630.xsd#irtc_AccruedHealthBenefitsLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_irtc_AccruedHealthBenefitsLiability_019f44ea-1ff2-7bea-9802-bb4560a5f067" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForLegalSettlements_019f44ea-1ff2-7dd5-9cb6-fb013b137bbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForLegalSettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_PaymentsForLegalSettlements_019f44ea-1ff2-7dd5-9cb6-fb013b137bbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrentAndNoncurrent_019f44ea-1ff2-70e2-8874-69e46c75639b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrentAndNoncurrent_019f44ea-1ff2-70e2-8874-69e46c75639b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimatedInsuranceRecoveries_019f6caf-0668-77f2-8b52-c871e556151c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimatedInsuranceRecoveries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_EstimatedInsuranceRecoveries_019f6caf-0668-77f2-8b52-c871e556151c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_EstimatedInsuranceRecoveriesIncurred_019f6cd3-42e6-79c9-b54c-1b26cfa4e721" xlink:href="irtc-20260630.xsd#irtc_EstimatedInsuranceRecoveriesIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_irtc_EstimatedInsuranceRecoveriesIncurred_019f6cd3-42e6-79c9-b54c-1b26cfa4e721" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementExpense_019f44ea-1ff2-7b09-89a5-a6371ae34ba8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationSettlementExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_LitigationSettlementExpense_019f44ea-1ff2-7b09-89a5-a6371ae34ba8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InsuranceRecoveries_019f44ea-1ff2-7c19-9a7d-55454740f31e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InsuranceRecoveries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_InsuranceRecoveries_019f44ea-1ff2-7c19-9a7d-55454740f31e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_LitigationSettlementFeeExpenseNetOfInsuranceRecoveries_019f6ccb-a225-7098-8bf5-b30efb7d7560" xlink:href="irtc-20260630.xsd#irtc_LitigationSettlementFeeExpenseNetOfInsuranceRecoveries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_irtc_LitigationSettlementFeeExpenseNetOfInsuranceRecoveries_019f6ccb-a225-7098-8bf5-b30efb7d7560" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_TechnologyLicenseAgreementUpfrontFee_019f44ea-6b59-7aa8-a265-6920126e6b51" xlink:href="irtc-20260630.xsd#irtc_TechnologyLicenseAgreementUpfrontFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_irtc_TechnologyLicenseAgreementUpfrontFee_019f44ea-6b59-7aa8-a265-6920126e6b51" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_PaymentsToAcquireConvertibleDebt_019f44ea-6b59-72d3-8a05-7f48e7063f4f" xlink:href="irtc-20260630.xsd#irtc_PaymentsToAcquireConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_irtc_PaymentsToAcquireConvertibleDebt_019f44ea-6b59-72d3-8a05-7f48e7063f4f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentDecreaseForgiveness_019f44ea-6b59-755f-bd21-0f9f0025d078" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentDecreaseForgiveness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_DebtInstrumentDecreaseForgiveness_019f44ea-6b59-755f-bd21-0f9f0025d078" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOff_019f44ea-6b59-7525-8fac-840061d9d572" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOff_019f44ea-6b59-7525-8fac-840061d9d572" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_019f44ea-6b59-78af-b3db-37033aae26b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_AssetImpairmentCharges_019f44ea-6b59-78af-b3db-37033aae26b3" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/COMMITMENTSANDCONTINGENCIESNarrativeDetails_1" xlink:type="simple" xlink:href="irtc-20260630.xsd#COMMITMENTSANDCONTINGENCIESNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/COMMITMENTSANDCONTINGENCIESNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseAxis_019f6cb0-a029-7818-9d73-c7e2205282f7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:to="loc_srt_LitigationCaseAxis_019f6cb0-a029-7818-9d73-c7e2205282f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019f6cb0-a029-7818-9d73-c7e2205282f7_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_LitigationCaseAxis_019f6cb0-a029-7818-9d73-c7e2205282f7" xlink:to="loc_srt_LitigationCaseTypeDomain_019f6cb0-a029-7818-9d73-c7e2205282f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019f6cb0-d9bd-792e-97d2-7418516918c3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_LitigationCaseAxis_019f6cb0-a029-7818-9d73-c7e2205282f7" xlink:to="loc_srt_LitigationCaseTypeDomain_019f6cb0-d9bd-792e-97d2-7418516918c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_ClassActionMember_019f6cb2-2359-72df-a0ac-372b91b5278e" xlink:href="irtc-20260630.xsd#irtc_ClassActionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_LitigationCaseTypeDomain_019f6cb0-d9bd-792e-97d2-7418516918c3" xlink:to="loc_irtc_ClassActionMember_019f6cb2-2359-72df-a0ac-372b91b5278e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_019f44ea-6b59-7a76-9271-a801f96706f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_019f44ea-6b59-7a76-9271-a801f96706f2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019f44ea-6b59-7a76-9271-a801f96706f2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019f44ea-6b59-7a76-9271-a801f96706f2" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019f44ea-6b59-7a76-9271-a801f96706f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019f44ea-6b59-7614-9b32-29243d6731ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019f44ea-6b59-7a76-9271-a801f96706f2" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019f44ea-6b59-7614-9b32-29243d6731ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleNotesPayableMember_019f44ea-6b59-77c9-b016-075c19905207" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleNotesPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019f44ea-6b59-7614-9b32-29243d6731ec" xlink:to="loc_us-gaap_ConvertibleNotesPayableMember_019f44ea-6b59-77c9-b016-075c19905207" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_MilestoneNotesMember_019f44ea-6b59-70a3-90c0-9aac9b7c050f" xlink:href="irtc-20260630.xsd#irtc_MilestoneNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019f44ea-6b59-7614-9b32-29243d6731ec" xlink:to="loc_irtc_MilestoneNotesMember_019f44ea-6b59-70a3-90c0-9aac9b7c050f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019f44ea-6b59-79ec-aa95-cc1498e1d482" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:to="loc_dei_LegalEntityAxis_019f44ea-6b59-79ec-aa95-cc1498e1d482" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019f44ea-6b59-79ec-aa95-cc1498e1d482_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019f44ea-6b59-79ec-aa95-cc1498e1d482" xlink:to="loc_dei_EntityDomain_019f44ea-6b59-79ec-aa95-cc1498e1d482_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019f44ea-6b59-7791-afd5-87dd4235df81" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019f44ea-6b59-79ec-aa95-cc1498e1d482" xlink:to="loc_dei_EntityDomain_019f44ea-6b59-7791-afd5-87dd4235df81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_BioIntelliSenseInc.Member_019f44ea-6b59-7046-b832-78ce4080fad0" xlink:href="irtc-20260630.xsd#irtc_BioIntelliSenseInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019f44ea-6b59-7791-afd5-87dd4235df81" xlink:to="loc_irtc_BioIntelliSenseInc.Member_019f44ea-6b59-7046-b832-78ce4080fad0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f44ea-6b59-7d2a-8b32-03b98baa4374" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019eb280-b211-7694-ac27-c372341cf1bb" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f44ea-6b59-7d2a-8b32-03b98baa4374" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f44ea-6b59-7d2a-8b32-03b98baa4374_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f44ea-6b59-7d2a-8b32-03b98baa4374" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f44ea-6b59-7d2a-8b32-03b98baa4374_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f44ea-6b59-7ac5-87c9-32c0499e0180" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f44ea-6b59-7d2a-8b32-03b98baa4374" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f44ea-6b59-7ac5-87c9-32c0499e0180" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_019f44ea-6b59-7185-ac4a-d9399094335a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f44ea-6b59-7ac5-87c9-32c0499e0180" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_019f44ea-6b59-7185-ac4a-d9399094335a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_AccruedHealthBenefitsLiability_019f44ea-1ff2-7bea-9802-bb4560a5f067" xlink:href="irtc-20260630.xsd#irtc_AccruedHealthBenefitsLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_irtc_AccruedHealthBenefitsLiability_019f44ea-1ff2-7bea-9802-bb4560a5f067" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForLegalSettlements_019f44ea-1ff2-7dd5-9cb6-fb013b137bbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForLegalSettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_PaymentsForLegalSettlements_019f44ea-1ff2-7dd5-9cb6-fb013b137bbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrentAndNoncurrent_019f44ea-1ff2-70e2-8874-69e46c75639b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrentAndNoncurrent_019f44ea-1ff2-70e2-8874-69e46c75639b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimatedInsuranceRecoveries_019f6caf-0668-77f2-8b52-c871e556151c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimatedInsuranceRecoveries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_EstimatedInsuranceRecoveries_019f6caf-0668-77f2-8b52-c871e556151c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_EstimatedInsuranceRecoveriesIncurred_019f6cd3-42e6-79c9-b54c-1b26cfa4e721" xlink:href="irtc-20260630.xsd#irtc_EstimatedInsuranceRecoveriesIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_irtc_EstimatedInsuranceRecoveriesIncurred_019f6cd3-42e6-79c9-b54c-1b26cfa4e721" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementExpense_019f44ea-1ff2-7b09-89a5-a6371ae34ba8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationSettlementExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_LitigationSettlementExpense_019f44ea-1ff2-7b09-89a5-a6371ae34ba8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InsuranceRecoveries_019f44ea-1ff2-7c19-9a7d-55454740f31e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InsuranceRecoveries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_InsuranceRecoveries_019f44ea-1ff2-7c19-9a7d-55454740f31e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_LitigationSettlementFeeExpenseNetOfInsuranceRecoveries_019f6ccb-a225-7098-8bf5-b30efb7d7560" xlink:href="irtc-20260630.xsd#irtc_LitigationSettlementFeeExpenseNetOfInsuranceRecoveries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_irtc_LitigationSettlementFeeExpenseNetOfInsuranceRecoveries_019f6ccb-a225-7098-8bf5-b30efb7d7560" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_TechnologyLicenseAgreementUpfrontFee_019f44ea-6b59-7aa8-a265-6920126e6b51" xlink:href="irtc-20260630.xsd#irtc_TechnologyLicenseAgreementUpfrontFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_irtc_TechnologyLicenseAgreementUpfrontFee_019f44ea-6b59-7aa8-a265-6920126e6b51" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_PaymentsToAcquireConvertibleDebt_019f44ea-6b59-72d3-8a05-7f48e7063f4f" xlink:href="irtc-20260630.xsd#irtc_PaymentsToAcquireConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_irtc_PaymentsToAcquireConvertibleDebt_019f44ea-6b59-72d3-8a05-7f48e7063f4f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentDecreaseForgiveness_019f44ea-6b59-755f-bd21-0f9f0025d078" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentDecreaseForgiveness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_DebtInstrumentDecreaseForgiveness_019f44ea-6b59-755f-bd21-0f9f0025d078" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOff_019f44ea-6b59-7525-8fac-840061d9d572" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOff_019f44ea-6b59-7525-8fac-840061d9d572" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_019f44ea-6b59-78af-b3db-37033aae26b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019eb280-b211-79fd-a75e-f90553a486f6" xlink:to="loc_us-gaap_AssetImpairmentCharges_019f44ea-6b59-78af-b3db-37033aae26b3" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/DEBTNarrativeDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#DEBTNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/DEBTNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019eb280-b211-74ea-a7ce-aca8b55e4ef9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_us-gaap_DebtInstrumentTable_019eb280-b211-74ea-a7ce-aca8b55e4ef9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-73eb-8c75-311d58d53c3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019eb280-b211-74ea-a7ce-aca8b55e4ef9" xlink:to="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-73eb-8c75-311d58d53c3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-73eb-8c75-311d58d53c3f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-73eb-8c75-311d58d53c3f" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-73eb-8c75-311d58d53c3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-73fa-84dc-35bf2ade8270" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-73eb-8c75-311d58d53c3f" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-73fa-84dc-35bf2ade8270" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_SeniorConvertibleNotesDue2029Member_019eb280-b211-7f96-94a4-392766b5d83e" xlink:href="irtc-20260630.xsd#irtc_SeniorConvertibleNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-73fa-84dc-35bf2ade8270" xlink:to="loc_irtc_SeniorConvertibleNotesDue2029Member_019eb280-b211-7f96-94a4-392766b5d83e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_ConvertibleNotesDue2029Member_019eb280-b211-7635-805f-47ee1f9f6e38" xlink:href="irtc-20260630.xsd#irtc_ConvertibleNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-73fa-84dc-35bf2ade8270" xlink:to="loc_irtc_ConvertibleNotesDue2029Member_019eb280-b211-7635-805f-47ee1f9f6e38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-74df-a319-b9803473ce07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019eb280-b211-74ea-a7ce-aca8b55e4ef9" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-74df-a319-b9803473ce07" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-74df-a319-b9803473ce07_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-74df-a319-b9803473ce07" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-74df-a319-b9803473ce07_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7703-a811-9f8c22f8f996" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-74df-a319-b9803473ce07" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7703-a811-9f8c22f8f996" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019eb280-b211-7394-9d96-7b3ec4c97991" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7703-a811-9f8c22f8f996" xlink:to="loc_us-gaap_ConvertibleDebtMember_019eb280-b211-7394-9d96-7b3ec4c97991" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentConversionTermAxis_019eb280-b211-704d-9bb7-adbc9755b666" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentConversionTermAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019eb280-b211-74ea-a7ce-aca8b55e4ef9" xlink:to="loc_irtc_DebtInstrumentConversionTermAxis_019eb280-b211-704d-9bb7-adbc9755b666" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentConversionTermDomain_019eb280-b211-704d-9bb7-adbc9755b666_default" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentConversionTermDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_irtc_DebtInstrumentConversionTermAxis_019eb280-b211-704d-9bb7-adbc9755b666" xlink:to="loc_irtc_DebtInstrumentConversionTermDomain_019eb280-b211-704d-9bb7-adbc9755b666_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentConversionTermDomain_019eb280-b211-78ce-94f0-c062738a3f42" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentConversionTermDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_irtc_DebtInstrumentConversionTermAxis_019eb280-b211-704d-9bb7-adbc9755b666" xlink:to="loc_irtc_DebtInstrumentConversionTermDomain_019eb280-b211-78ce-94f0-c062738a3f42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentConversionTermOneMember_019eb280-b211-7e0b-b0c3-ed465838e55d" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentConversionTermOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_irtc_DebtInstrumentConversionTermDomain_019eb280-b211-78ce-94f0-c062738a3f42" xlink:to="loc_irtc_DebtInstrumentConversionTermOneMember_019eb280-b211-7e0b-b0c3-ed465838e55d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentConversionTermTwoMember_019eb280-b211-7208-8a9d-337c03e073e6" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentConversionTermTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_irtc_DebtInstrumentConversionTermDomain_019eb280-b211-78ce-94f0-c062738a3f42" xlink:to="loc_irtc_DebtInstrumentConversionTermTwoMember_019eb280-b211-7208-8a9d-337c03e073e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019eb280-b211-7d12-9a7a-a70fe213e030" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019eb280-b211-74ea-a7ce-aca8b55e4ef9" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019eb280-b211-7d12-9a7a-a70fe213e030" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019eb280-b211-7d12-9a7a-a70fe213e030_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019eb280-b211-7d12-9a7a-a70fe213e030" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019eb280-b211-7d12-9a7a-a70fe213e030_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019eb280-b211-7610-8592-48444ab8b34d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019eb280-b211-7d12-9a7a-a70fe213e030" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019eb280-b211-7610-8592-48444ab8b34d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_A2029CappedCallTransactionsMember_019eb280-b211-7de7-86e6-4215a577be00" xlink:href="irtc-20260630.xsd#irtc_A2029CappedCallTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019eb280-b211-7610-8592-48444ab8b34d" xlink:to="loc_irtc_A2029CappedCallTransactionsMember_019eb280-b211-7de7-86e6-4215a577be00" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019eb280-b211-739a-95ef-97b3dd74fdaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019eb280-b211-739a-95ef-97b3dd74fdaf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019eb280-b211-70ae-81be-695ba7ea7ea2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019eb280-b211-70ae-81be-695ba7ea7ea2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentOptionToPurchaseConvertibleDebtAdditionalPurchaseAmount_019eb280-b211-7e3e-b8f6-e544c4fd24fe" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentOptionToPurchaseConvertibleDebtAdditionalPurchaseAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_irtc_DebtInstrumentOptionToPurchaseConvertibleDebtAdditionalPurchaseAmount_019eb280-b211-7e3e-b8f6-e544c4fd24fe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromConvertibleDebt_019eb280-b211-7735-927e-da32de6d0d56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_us-gaap_ProceedsFromConvertibleDebt_019eb280-b211-7735-927e-da32de6d0d56" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_019eb280-b211-7bc6-bc19-c64bbd16b037" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_019eb280-b211-7bc6-bc19-c64bbd16b037" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_019eb280-b211-7295-92ef-912d7d52d286" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_019eb280-b211-7295-92ef-912d7d52d286" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentCovenantRepurchasePricePercentage_019eb280-b211-7177-a3be-1dc6052bf46a" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentCovenantRepurchasePricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_irtc_DebtInstrumentCovenantRepurchasePricePercentage_019eb280-b211-7177-a3be-1dc6052bf46a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentTermsOfConversionFeatureConvertibleUnderCertainCircumstancesConversionAmount_019eb280-b211-7a25-84f7-85deb37d7a59" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentTermsOfConversionFeatureConvertibleUnderCertainCircumstancesConversionAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_irtc_DebtInstrumentTermsOfConversionFeatureConvertibleUnderCertainCircumstancesConversionAmount_019eb280-b211-7a25-84f7-85deb37d7a59" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_019eb280-b211-7eca-a20a-b48c89d6a9ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_019eb280-b211-7eca-a20a-b48c89d6a9ac" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_019eb280-b211-7776-9bad-d30159c91dea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_019eb280-b211-7776-9bad-d30159c91dea" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_019eb280-b211-7742-82e3-cfd82fc09c3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_019eb280-b211-7742-82e3-cfd82fc09c3f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentConvertibleRegardlessOfCircumstancesTermsOfConversionFeatureConversionAmount_019eb280-b211-7010-8edc-4c06625ee4c9" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentConvertibleRegardlessOfCircumstancesTermsOfConversionFeatureConversionAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_irtc_DebtInstrumentConvertibleRegardlessOfCircumstancesTermsOfConversionFeatureConversionAmount_019eb280-b211-7010-8edc-4c06625ee4c9" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentConvertedAmount_019f6cd6-1592-76e3-a5b0-10eb8952636e" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentConvertedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_irtc_DebtInstrumentConvertedAmount_019f6cd6-1592-76e3-a5b0-10eb8952636e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentRedemptionCovenantPercentOfConversionPriceLastReportedSalePriceOfCommonStock_019eb280-b211-7266-b06e-f51980d2ddf8" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentRedemptionCovenantPercentOfConversionPriceLastReportedSalePriceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_irtc_DebtInstrumentRedemptionCovenantPercentOfConversionPriceLastReportedSalePriceOfCommonStock_019eb280-b211-7266-b06e-f51980d2ddf8" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_019eb280-b211-7065-9fc2-d9eabb736a6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_019eb280-b211-7065-9fc2-d9eabb736a6f" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentCappedCallsPriceCap_019eb280-b211-7090-aacd-1cc4bf5f4919" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentCappedCallsPriceCap"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_irtc_DebtInstrumentCappedCallsPriceCap_019eb280-b211-7090-aacd-1cc4bf5f4919" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_DebtInstrumentCappedCallsPremiumPercentageOverClosingPrice_019eb280-b211-7b2d-be23-647a7b88d28b" xlink:href="irtc-20260630.xsd#irtc_DebtInstrumentCappedCallsPremiumPercentageOverClosingPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_irtc_DebtInstrumentCappedCallsPremiumPercentageOverClosingPrice_019eb280-b211-7b2d-be23-647a7b88d28b" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharePrice_019eb280-b211-7958-87cf-87b1c8bf1356" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_us-gaap_SharePrice_019eb280-b211-7958-87cf-87b1c8bf1356" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_PurchasesOfCappedCallsTransactions_019eb280-b211-7fd9-9b4c-b437eeac058d" xlink:href="irtc-20260630.xsd#irtc_PurchasesOfCappedCallsTransactions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7a69-997e-67d435e6fbf6" xlink:to="loc_irtc_PurchasesOfCappedCallsTransactions_019eb280-b211-7fd9-9b4c-b437eeac058d" xlink:type="arc" order="18"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/DEBTScheduleofConvertibleDebtDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#DEBTScheduleofConvertibleDebtDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/DEBTScheduleofConvertibleDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7d15-9071-5442027ed75d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019eb280-b211-7656-a5fc-d320d4492275" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7d15-9071-5442027ed75d" xlink:to="loc_us-gaap_DebtInstrumentTable_019eb280-b211-7656-a5fc-d320d4492275" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-75e8-966b-dc9b29886a56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019eb280-b211-7656-a5fc-d320d4492275" xlink:to="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-75e8-966b-dc9b29886a56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-75e8-966b-dc9b29886a56_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-75e8-966b-dc9b29886a56" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-75e8-966b-dc9b29886a56_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-7c85-93ec-f5e8f7236383" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-75e8-966b-dc9b29886a56" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-7c85-93ec-f5e8f7236383" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_ConvertibleNotesDue2029Member_019eb280-b211-7820-81ec-5a0c22138ed4" xlink:href="irtc-20260630.xsd#irtc_ConvertibleNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-7c85-93ec-f5e8f7236383" xlink:to="loc_irtc_ConvertibleNotesDue2029Member_019eb280-b211-7820-81ec-5a0c22138ed4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-790d-a330-f95febef9d87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019eb280-b211-7656-a5fc-d320d4492275" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-790d-a330-f95febef9d87" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-790d-a330-f95febef9d87_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-790d-a330-f95febef9d87" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-790d-a330-f95febef9d87_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7603-bf7e-0f6ecf3a9426" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-790d-a330-f95febef9d87" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7603-bf7e-0f6ecf3a9426" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019eb280-b211-79d1-8041-ee98ee237005" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7603-bf7e-0f6ecf3a9426" xlink:to="loc_us-gaap_ConvertibleDebtMember_019eb280-b211-79d1-8041-ee98ee237005" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019eb280-b211-7c53-a101-35410e07aeb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7d15-9071-5442027ed75d" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019eb280-b211-7c53-a101-35410e07aeb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_019eb280-b211-7012-bef2-c9d22ea99d52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7d15-9071-5442027ed75d" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_019eb280-b211-7012-bef2-c9d22ea99d52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleLongTermNotesPayable_019eb280-b211-76ba-96f2-f216b1f25f7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleLongTermNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7d15-9071-5442027ed75d" xlink:to="loc_us-gaap_ConvertibleLongTermNotesPayable_019eb280-b211-76ba-96f2-f216b1f25f7a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/DEBTScheduleofComponentsofInterestExpenseandtheEffectiveInterestRatesDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#DEBTScheduleofComponentsofInterestExpenseandtheEffectiveInterestRatesDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/DEBTScheduleofComponentsofInterestExpenseandtheEffectiveInterestRatesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7b20-b8b7-dce1d2785524" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019eb280-b211-74a9-a55e-3894283381ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7b20-b8b7-dce1d2785524" xlink:to="loc_us-gaap_DebtInstrumentTable_019eb280-b211-74a9-a55e-3894283381ad" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-777b-a4f8-1bf8ec173d0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019eb280-b211-74a9-a55e-3894283381ad" xlink:to="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-777b-a4f8-1bf8ec173d0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-777b-a4f8-1bf8ec173d0a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-777b-a4f8-1bf8ec173d0a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-777b-a4f8-1bf8ec173d0a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-77b6-a199-b1c018a87e8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb280-b211-777b-a4f8-1bf8ec173d0a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-77b6-a199-b1c018a87e8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_ConvertibleNotesDue2029Member_019eb280-b211-7c46-809a-4145faa731c9" xlink:href="irtc-20260630.xsd#irtc_ConvertibleNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019eb280-b211-77b6-a199-b1c018a87e8c" xlink:to="loc_irtc_ConvertibleNotesDue2029Member_019eb280-b211-7c46-809a-4145faa731c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-7a02-a382-006a70556bd1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019eb280-b211-74a9-a55e-3894283381ad" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-7a02-a382-006a70556bd1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7a02-a382-006a70556bd1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-7a02-a382-006a70556bd1" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7a02-a382-006a70556bd1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7abc-8242-828815f6bb95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb280-b211-7a02-a382-006a70556bd1" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7abc-8242-828815f6bb95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019eb280-b211-7931-8c13-92ef442e5dd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019eb280-b211-7abc-8242-828815f6bb95" xlink:to="loc_us-gaap_ConvertibleDebtMember_019eb280-b211-7931-8c13-92ef442e5dd2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebtExcludingAmortization_019eb280-b211-70ab-bb79-13dd071a194b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseDebtExcludingAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7b20-b8b7-dce1d2785524" xlink:to="loc_us-gaap_InterestExpenseDebtExcludingAmortization_019eb280-b211-70ab-bb79-13dd071a194b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_019eb280-b211-7e6d-82d1-991cdf24c097" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7b20-b8b7-dce1d2785524" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_019eb280-b211-7e6d-82d1-991cdf24c097" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_019eb280-b211-7231-96b2-71f98ef335ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7b20-b8b7-dce1d2785524" xlink:to="loc_us-gaap_InterestExpenseDebt_019eb280-b211-7231-96b2-71f98ef335ac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019eb280-b211-7758-a881-ef878f84e21e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb280-b211-7b20-b8b7-dce1d2785524" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019eb280-b211-7758-a881-ef878f84e21e" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/STOCKBASEDCOMPENSATIONScheduleofStockBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#STOCKBASEDCOMPENSATIONScheduleofStockBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/STOCKBASEDCOMPENSATIONScheduleofStockBasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019eb280-b211-7a12-a23c-19390f28a744" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019eb280-b211-7a11-9830-64768113cb5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019eb280-b211-7a12-a23c-19390f28a744" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019eb280-b211-7a11-9830-64768113cb5b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019eb280-b211-759e-816a-15d7137b9543" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019eb280-b211-7a11-9830-64768113cb5b" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019eb280-b211-759e-816a-15d7137b9543" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eb280-b211-72c1-bad4-66d3bfa4752b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019eb280-b211-7a12-a23c-19390f28a744" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eb280-b211-72c1-bad4-66d3bfa4752b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/STOCKBASEDCOMPENSATIONScheduleofStockBasedCompensationExpenseDetails_1" xlink:type="simple" xlink:href="irtc-20260630.xsd#STOCKBASEDCOMPENSATIONScheduleofStockBasedCompensationExpenseDetails_1"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/STOCKBASEDCOMPENSATIONScheduleofStockBasedCompensationExpenseDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019eb280-b211-7a12-a23c-19390f28a744" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019eb280-b211-7a11-9830-64768113cb5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019eb280-b211-7a12-a23c-19390f28a744" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019eb280-b211-7a11-9830-64768113cb5b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eb280-b211-72c1-bad4-66d3bfa4752b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019eb280-b211-7a12-a23c-19390f28a744" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019eb280-b211-72c1-bad4-66d3bfa4752b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/STOCKBASEDCOMPENSATIONNarrativeDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#STOCKBASEDCOMPENSATIONNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/STOCKBASEDCOMPENSATIONNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eb280-b211-7546-9c78-daebd10c0cd7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eb280-b211-7546-9c78-daebd10c0cd7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019eb280-b211-72d8-8a03-475242a98189" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eb280-b211-7546-9c78-daebd10c0cd7" xlink:to="loc_us-gaap_AwardTypeAxis_019eb280-b211-72d8-8a03-475242a98189" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eb280-b211-72d8-8a03-475242a98189_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019eb280-b211-72d8-8a03-475242a98189" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eb280-b211-72d8-8a03-475242a98189_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eb280-b211-7c73-bca8-d2dc2912f4d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019eb280-b211-72d8-8a03-475242a98189" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eb280-b211-7c73-bca8-d2dc2912f4d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019eb280-b211-7a26-b76e-7eb99c41aec0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eb280-b211-7c73-bca8-d2dc2912f4d8" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019eb280-b211-7a26-b76e-7eb99c41aec0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019eb280-b211-7cec-b99d-f3b89ad3214c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019eb280-b211-7c73-bca8-d2dc2912f4d8" xlink:to="loc_us-gaap_PerformanceSharesMember_019eb280-b211-7cec-b99d-f3b89ad3214c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019eb280-b211-7cdf-9e36-d3b43fa109df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eb280-b211-7546-9c78-daebd10c0cd7" xlink:to="loc_us-gaap_PlanNameAxis_019eb280-b211-7cdf-9e36-d3b43fa109df" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019eb280-b211-7cdf-9e36-d3b43fa109df_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019eb280-b211-7cdf-9e36-d3b43fa109df" xlink:to="loc_us-gaap_PlanNameDomain_019eb280-b211-7cdf-9e36-d3b43fa109df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019eb280-b211-7e95-bd2c-e1bf055f5dfd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019eb280-b211-7cdf-9e36-d3b43fa109df" xlink:to="loc_us-gaap_PlanNameDomain_019eb280-b211-7e95-bd2c-e1bf055f5dfd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_EmployeeStockPurchasePlanMember_019eb280-b211-7f17-bd81-09940a159783" xlink:href="irtc-20260630.xsd#irtc_EmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019eb280-b211-7e95-bd2c-e1bf055f5dfd" xlink:to="loc_irtc_EmployeeStockPurchasePlanMember_019eb280-b211-7f17-bd81-09940a159783" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019eb280-b211-7849-b3bb-7bf2dff7c810" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019eb280-b211-7546-9c78-daebd10c0cd7" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019eb280-b211-7849-b3bb-7bf2dff7c810" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eb280-b211-7849-b3bb-7bf2dff7c810_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019eb280-b211-7849-b3bb-7bf2dff7c810" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eb280-b211-7849-b3bb-7bf2dff7c810_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eb280-b211-7cf3-a2b7-7c4679a3cea9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019eb280-b211-7849-b3bb-7bf2dff7c810" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eb280-b211-7cf3-a2b7-7c4679a3cea9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_019eb280-b211-7b7e-bacf-89333c90a03f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019eb280-b211-7cf3-a2b7-7c4679a3cea9" xlink:to="loc_us-gaap_EmployeeStockMember_019eb280-b211-7b7e-bacf-89333c90a03f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019eb280-b211-7b25-b2dd-8fbaf537b628" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019eb280-b211-7b25-b2dd-8fbaf537b628" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019eb280-b211-7725-965c-f02f7bc3de60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019eb280-b211-7725-965c-f02f7bc3de60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019eb280-b211-7b96-82a8-f15ff33506bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019eb280-b211-7b96-82a8-f15ff33506bb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019eb280-b211-7f0d-8ed7-7d50a4291a9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019eb280-b211-7f0d-8ed7-7d50a4291a9d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumCapacityPercentage_019eb280-b211-7705-ba8c-ca2e9099f490" xlink:href="irtc-20260630.xsd#irtc_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumCapacityPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:to="loc_irtc_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumCapacityPercentage_019eb280-b211-7705-ba8c-ca2e9099f490" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019eb280-b211-728d-a768-1c8eb61d923f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019eb280-b211-728d-a768-1c8eb61d923f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019eb280-b211-75b0-97b4-2e7c841a0a99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019eb280-b211-75b0-97b4-2e7c841a0a99" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019eb280-b211-74a3-b4ae-665033d00474" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019eb280-b211-74a3-b4ae-665033d00474" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019eb280-b211-7620-ab72-fe7fa4a8f8c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019eb280-b211-7620-ab72-fe7fa4a8f8c9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019eb280-b211-73ec-b187-e40c64873e2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019eb280-b211-73ec-b187-e40c64873e2a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019eb280-b211-7d4a-a4d6-787704ec2952" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019eb280-b211-7e49-82bf-42ca81f6bcd4" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019eb280-b211-7d4a-a4d6-787704ec2952" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/NETLOSSPERCOMMONSHAREScheduleofAntidilutiveSecuritiesExcludedfromDilutedNetLossperCommonShareDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#NETLOSSPERCOMMONSHAREScheduleofAntidilutiveSecuritiesExcludedfromDilutedNetLossperCommonShareDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/NETLOSSPERCOMMONSHAREScheduleofAntidilutiveSecuritiesExcludedfromDilutedNetLossperCommonShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019eb280-b211-7807-9612-5758003f00cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019eb280-b211-72be-8e40-b850df1ea791" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019eb280-b211-7807-9612-5758003f00cc" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019eb280-b211-72be-8e40-b850df1ea791" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019eb280-b211-76e3-8fa9-8fb3660ac403" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019eb280-b211-72be-8e40-b850df1ea791" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019eb280-b211-76e3-8fa9-8fb3660ac403" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eb280-b211-76e3-8fa9-8fb3660ac403_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019eb280-b211-76e3-8fa9-8fb3660ac403" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eb280-b211-76e3-8fa9-8fb3660ac403_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eb280-b211-7899-881f-deb99cc7e6ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019eb280-b211-76e3-8fa9-8fb3660ac403" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eb280-b211-7899-881f-deb99cc7e6ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019eb280-b211-7696-8f6e-010e1f14a6f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eb280-b211-7899-881f-deb99cc7e6ee" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019eb280-b211-7696-8f6e-010e1f14a6f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_RestrictedStockUnitsAndPerformanceBasedRestrictedStockUnitsMember_019eb280-b211-70c5-9fcd-fb4029a1de60" xlink:href="irtc-20260630.xsd#irtc_RestrictedStockUnitsAndPerformanceBasedRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eb280-b211-7899-881f-deb99cc7e6ee" xlink:to="loc_irtc_RestrictedStockUnitsAndPerformanceBasedRestrictedStockUnitsMember_019eb280-b211-70c5-9fcd-fb4029a1de60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_SeniorConvertibleNotesMember_019eb280-b211-7c30-ab67-b63443611be5" xlink:href="irtc-20260630.xsd#irtc_SeniorConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019eb280-b211-7899-881f-deb99cc7e6ee" xlink:to="loc_irtc_SeniorConvertibleNotesMember_019eb280-b211-7c30-ab67-b63443611be5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019eb280-b211-79ac-b409-52531e3f451b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019eb280-b211-7807-9612-5758003f00cc" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019eb280-b211-79ac-b409-52531e3f451b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.irhythmtec.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="irtc-20260630.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://www.irhythmtec.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_019eb280-b2d8-75bf-a77e-457b64eadfcd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_019eb280-b2d8-7598-a842-7c3db7529636" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_019eb280-b2d8-75bf-a77e-457b64eadfcd" xlink:to="loc_us-gaap_SubsequentEventTable_019eb280-b2d8-7598-a842-7c3db7529636" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019eb280-b2d8-71d1-8ac5-0bd3baa5af50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019eb280-b2d8-7598-a842-7c3db7529636" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019eb280-b2d8-71d1-8ac5-0bd3baa5af50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019eb280-b2d8-71d1-8ac5-0bd3baa5af50_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019eb280-b2d8-71d1-8ac5-0bd3baa5af50" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019eb280-b2d8-71d1-8ac5-0bd3baa5af50_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019eb280-b2d8-79a8-8730-540b28583baf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019eb280-b2d8-71d1-8ac5-0bd3baa5af50" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019eb280-b2d8-79a8-8730-540b28583baf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019eb280-b2d8-7d3a-888a-44fb7669a576" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019eb280-b2d8-79a8-8730-540b28583baf" xlink:to="loc_us-gaap_SubsequentEventMember_019eb280-b2d8-7d3a-888a-44fb7669a576" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019fc640-3f7a-7b75-ae01-ec4a8ed1872d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019eb280-b2d8-7598-a842-7c3db7529636" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019fc640-3f7a-7b75-ae01-ec4a8ed1872d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fc640-3f7a-7b75-ae01-ec4a8ed1872d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019fc640-3f7a-7b75-ae01-ec4a8ed1872d" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fc640-3f7a-7b75-ae01-ec4a8ed1872d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fc640-3f7a-7c2d-ae24-c86de39a1aae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019fc640-3f7a-7b75-ae01-ec4a8ed1872d" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fc640-3f7a-7c2d-ae24-c86de39a1aae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_BaxterSettlementAgreementMember_019fc640-3f7a-766b-b661-e938aaeaca73" xlink:href="irtc-20260630.xsd#irtc_BaxterSettlementAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fc640-3f7a-7c2d-ae24-c86de39a1aae" xlink:to="loc_irtc_BaxterSettlementAgreementMember_019fc640-3f7a-766b-b661-e938aaeaca73" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fb9fb-6bfe-77d2-a1c4-3f4667d44757" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019eb280-b2d8-7598-a842-7c3db7529636" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fb9fb-6bfe-77d2-a1c4-3f4667d44757" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fb9fb-6bfe-77d2-a1c4-3f4667d44757_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fb9fb-6bfe-77d2-a1c4-3f4667d44757" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fb9fb-6bfe-77d2-a1c4-3f4667d44757_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fb9fb-93a1-79eb-88ce-9d678d827d90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fb9fb-6bfe-77d2-a1c4-3f4667d44757" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fb9fb-93a1-79eb-88ce-9d678d827d90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_VitalConnectMember_019fba1a-5fb4-7c0c-bd14-8e1eee5fceae" xlink:href="irtc-20260630.xsd#irtc_VitalConnectMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fb9fb-93a1-79eb-88ce-9d678d827d90" xlink:to="loc_irtc_VitalConnectMember_019fba1a-5fb4-7c0c-bd14-8e1eee5fceae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_019fc640-3f7a-75a1-83b7-d177b2a0d705" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationSettlementAmountAwardedToOtherParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019eb280-b2d8-75bf-a77e-457b64eadfcd" xlink:to="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_019fc640-3f7a-75a1-83b7-d177b2a0d705" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_LicensePaymentAmount_019fc640-3f7a-77ea-a5f1-a741efb25bd9" xlink:href="irtc-20260630.xsd#irtc_LicensePaymentAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019eb280-b2d8-75bf-a77e-457b64eadfcd" xlink:to="loc_irtc_LicensePaymentAmount_019fc640-3f7a-77ea-a5f1-a741efb25bd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019fc640-3f7a-7708-bb10-bad86eb8bdaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019eb280-b2d8-75bf-a77e-457b64eadfcd" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019fc640-3f7a-7708-bb10-bad86eb8bdaf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_019fcfdc-3966-7ccb-9171-105310024319" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019eb280-b2d8-75bf-a77e-457b64eadfcd" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_019fcfdc-3966-7ccb-9171-105310024319" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019fc640-3f7a-72cc-9fdd-a59204206406" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019eb280-b2d8-75bf-a77e-457b64eadfcd" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019fc640-3f7a-72cc-9fdd-a59204206406" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_BusinessCombinationTerminationFee_019fc640-3f7a-787d-b6c8-cbd13a5f7cfb" xlink:href="irtc-20260630.xsd#irtc_BusinessCombinationTerminationFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019eb280-b2d8-75bf-a77e-457b64eadfcd" xlink:to="loc_irtc_BusinessCombinationTerminationFee_019fc640-3f7a-787d-b6c8-cbd13a5f7cfb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_BusinessCombinationInterimFinancingInitialFundingAmount_019fc640-3f7a-7d21-9319-79bdc6c5f856" xlink:href="irtc-20260630.xsd#irtc_BusinessCombinationInterimFinancingInitialFundingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019eb280-b2d8-75bf-a77e-457b64eadfcd" xlink:to="loc_irtc_BusinessCombinationInterimFinancingInitialFundingAmount_019fc640-3f7a-7d21-9319-79bdc6c5f856" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_irtc_BusinessCombinationInterimFinancingMaximumAmount_019fc640-3f7a-75a4-a3cc-d2b7b1d13fd1" xlink:href="irtc-20260630.xsd#irtc_BusinessCombinationInterimFinancingMaximumAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019eb280-b2d8-75bf-a77e-457b64eadfcd" xlink:to="loc_irtc_BusinessCombinationInterimFinancingMaximumAmount_019fc640-3f7a-75a4-a3cc-d2b7b1d13fd1" xlink:type="arc" order="7"/>
  </link:definitionLink>
</link:linkbase>
