0001223026 2025-05-01 2026-04-30 0001223026 2026-04-30 0001223026 pmhifi:RiskMember 2025-05-01 2026-04-30 0001223026 pmhifi:CommonSharesMember 2025-05-01 2026-04-30 0001223026 pmhifi:CommonSharesMember 2024-05-01 2025-04-30 shares iso4217:USD shares 0001223026 false N-CSR Pioneer Municipal High Income Fund, Inc. 0.19 the Fund has been operating under a Plan of Liquidation and Dissolution, and is in the process of winding up its business and affairs, paying its liabilities and distributing its remaining assets to stockholders (see Note 8). Accordingly, the Fund no longer pursues its stated investment objective, complies with its investment limitations or engages in normal business activities. <table style="text-align:start; border-collapse:collapse;empty-cells:show;margin-top:0pt;width:100%"> <tr style="page-break-inside:avoid"> <td style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9pt; font-style: normal; line-height: 12pt; padding-left: 0pt; padding-right: 2pt; text-align: left; text-decoration: none; text-transform: none; vertical-align: top; white-space: nowrap; width: 3.8%;"><div style="font-weight:bolder;display:inline;">E. </div></td> <td style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9pt; font-style: normal; line-height: 12pt; padding-left: 2pt; text-align: left; text-decoration: none; text-transform: none; vertical-align: top; white-space: nowrap; width: 96.2%;"><div style="font-weight:bolder;display:inline;">Risks </div></td></tr> <tr style="page-break-inside:avoid"> <td style="line-height:0pt;padding-bottom:0pt;padding-left:0pt;padding-right:2pt;text-align:left;vertical-align:top;width:3.80%">  </td> <td style="color:#000000;font-family:Arial;font-size:9pt;font-style:Normal;font-weight:Normal;line-height:12pt;padding-bottom:0pt;padding-left:2pt;text-align:left;text-decoration:none;text-transform:none;vertical-align:top; width:96.20%">Prior to the Fund's liquidation (See Note 8), the Fund invested substantially all of its assets in municipal securities. The municipal bond market can be susceptible to unusual volatility, particularly for lower-rated and unrated securities. Liquidity can be reduced unpredictably in response to overall economic conditions or credit tightening. Municipal issuers may be adversely affected by rising health care costs, increasing unfunded pension liabilities, and by the phasing out of federal programs providing financial support. Unfavorable conditions and developments relating to projects financed with municipal securities can result in lower revenues to issuers of municipal securities, potentially resulting in defaults. Issuers often depend on revenues from these projects to make principal and interest payments. The value of municipal securities can also be adversely affected by changes in the financial condition of one or more individual municipal issuers or insurers of municipal issuers, regulatory and political developments, tax law changes or other legislative actions, and by uncertainties and public perceptions </td></tr></table> <table cellpadding="7" cellspacing="0" style="text-align:start; border-collapse:collapse;empty-cells:show;margin-top:0pt;width:100%"> <tr style="page-break-inside:avoid"> <td style="line-height:0pt;padding-left:0pt;padding-right:2pt;text-align:left;vertical-align:top;width:3.80%">  </td> <td style="color:#000000;font-family:Arial;font-size:9pt;font-style:Normal;font-weight:Normal;line-height:12pt;padding-left:2pt;text-align:left;text-decoration:none;text-transform:none;vertical-align:top;width:96.20%">concerning these and other factors. Municipal securities may be more susceptible to down-grades or defaults during recessions or similar periods of economic stress. Financial difficulties of municipal issuers may continue or get worse, particularly in the event of economic or market turmoil or a recession. To the extent the Fund invests significantly in a single state (including California and Massachusetts), city, territory (including Puerto Rico), or region, or in securities the payments on which are dependent upon a single project or source of revenues, or that relate to a sector or industry, including health care facilities, education, transportation, special revenues and pollution control, the Fund will be more susceptible to associated risks and developments. </td></tr> <tr style="page-break-inside:avoid"> <td style="line-height:0pt;padding-left:0pt;padding-right:2pt;text-align:left;vertical-align:top;width:3.80%">  </td> <td style="color:#000000;font-family:Arial;font-size:9pt;font-style:Normal;font-weight:Normal;line-height:12pt;padding-left:2pt;text-align:left;text-decoration:none;text-transform:none;vertical-align:top;width:96.20%">The Fund invested in below investment grade (high yield) municipal securities. Debt securities rated below investment grade are commonly referred to as “junk bonds” and are considered speculative with respect to the issuer’s capacity to pay interest and repay principal. These securities involve greater risk of loss, are subject to greater price volatility, and may be less liquid and more difficult to value, especially during periods of economic uncertainty or change, than higher rated debt securities. </td></tr> <tr style="page-break-inside:avoid"> <td style="line-height:0pt;padding-left:0pt;padding-right:2pt;text-align:left;vertical-align:top;width:3.80%">  </td> <td style="color:#000000;font-family:Arial;font-size:9pt;font-style:Normal;font-weight:Normal;line-height:12pt;padding-left:2pt;text-align:left;text-decoration:none;text-transform:none;vertical-align:top;width:96.20%">The market prices of the Fund’s fixed income securities may fluctuate significantly when interest rates change. The value of your investment will generally go down when interest rates rise. A rise in rates tends to have a greater impact on the prices of longer term or duration securities. For example, if interest rates increase by 1%, the value of a Fund’s portfolio with a portfolio duration of ten years would be expected to decrease by 10%, all other things being equal. A general rise in interest rates could adversely affect the price and liquidity of fixed income securities. The maturity of a security may be significantly longer than its effective duration. A security’s maturity and other features may be more relevant than its effective duration in determining the security’s sensitivity to other factors affecting the issuer or markets generally, such as changes in credit quality or in the yield premium that the market may establish for certain types of securities (sometimes called “credit spread”). In general, the longer its maturity the more a security may be susceptible to these factors. When the credit spread for a fixed income security goes up, or “widens”, the value of the security will generally go down. </td></tr> <tr style="page-break-inside:avoid"> <td style="line-height:0pt;padding-bottom:0pt;padding-left:0pt;padding-right:2pt;text-align:left;vertical-align:top;width:3.80%">  </td> <td style="color:#000000;font-family:Arial;font-size:9pt;font-style:Normal;font-weight:Normal;line-height:12pt;padding-bottom:0pt;padding-left:2pt;text-align:left;text-decoration:none;text-transform:none;vertical-align:top; width:96.20%">If an issuer or guarantor of a security held by the Fund or a counterparty to a financial contract with the Fund defaults on its obligation to pay principal and/or interest, has its credit rating downgraded or is perceived to be less creditworthy, or the credit quality </td></tr></table> <table cellpadding="7" cellspacing="0" style="text-align:start; border-collapse:collapse;empty-cells:show;margin-top:0pt;width:100%"> <tr style="page-break-inside:avoid"> <td style="line-height:0pt;padding-left:0pt;padding-right:2pt;text-align:left;vertical-align:top;width:3.80%">  </td> <td style="color:#000000;font-family:Arial;font-size:9pt;font-style:Normal;font-weight:Normal;line-height:12pt;padding-left:2pt;text-align:left;text-decoration:none;text-transform:none;vertical-align:top;width:96.20%">or value of any underlying assets declines, the value of your investment will typically decline. Changes in actual or perceived creditworthiness may occur quickly. The Fund could be delayed or hindered in its enforcement of rights against an issuer, guarantor or counterparty. </td></tr></table> <table style="text-align:start; border-collapse:collapse;empty-cells:show;margin-top:0pt;width:100%"> <tr style="page-break-inside:avoid"> <td style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9pt; font-style: normal; line-height: 12pt; padding-left: 0pt; padding-right: 2pt; text-align: left; text-decoration: none; text-transform: none; vertical-align: top; white-space: nowrap; width: 3.8%;"><div style="font-weight:bolder;display:inline;">E. </div></td> <td style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9pt; font-style: normal; line-height: 12pt; padding-left: 2pt; text-align: left; text-decoration: none; text-transform: none; vertical-align: top; white-space: nowrap; width: 96.2%;"><div style="font-weight:bolder;display:inline;">Risks </div></td></tr> <tr style="page-break-inside:avoid"> <td style="line-height:0pt;padding-bottom:0pt;padding-left:0pt;padding-right:2pt;text-align:left;vertical-align:top;width:3.80%">  </td> <td style="color:#000000;font-family:Arial;font-size:9pt;font-style:Normal;font-weight:Normal;line-height:12pt;padding-bottom:0pt;padding-left:2pt;text-align:left;text-decoration:none;text-transform:none;vertical-align:top; width:96.20%">Prior to the Fund's liquidation (See Note 8), the Fund invested substantially all of its assets in municipal securities. The municipal bond market can be susceptible to unusual volatility, particularly for lower-rated and unrated securities. Liquidity can be reduced unpredictably in response to overall economic conditions or credit tightening. Municipal issuers may be adversely affected by rising health care costs, increasing unfunded pension liabilities, and by the phasing out of federal programs providing financial support. Unfavorable conditions and developments relating to projects financed with municipal securities can result in lower revenues to issuers of municipal securities, potentially resulting in defaults. Issuers often depend on revenues from these projects to make principal and interest payments. The value of municipal securities can also be adversely affected by changes in the financial condition of one or more individual municipal issuers or insurers of municipal issuers, regulatory and political developments, tax law changes or other legislative actions, and by uncertainties and public perceptions </td></tr></table> <table cellpadding="7" cellspacing="0" style="text-align:start; border-collapse:collapse;empty-cells:show;margin-top:0pt;width:100%"> <tr style="page-break-inside:avoid"> <td style="line-height:0pt;padding-left:0pt;padding-right:2pt;text-align:left;vertical-align:top;width:3.80%">  </td> <td style="color:#000000;font-family:Arial;font-size:9pt;font-style:Normal;font-weight:Normal;line-height:12pt;padding-left:2pt;text-align:left;text-decoration:none;text-transform:none;vertical-align:top;width:96.20%">concerning these and other factors. Municipal securities may be more susceptible to down-grades or defaults during recessions or similar periods of economic stress. Financial difficulties of municipal issuers may continue or get worse, particularly in the event of economic or market turmoil or a recession. To the extent the Fund invests significantly in a single state (including California and Massachusetts), city, territory (including Puerto Rico), or region, or in securities the payments on which are dependent upon a single project or source of revenues, or that relate to a sector or industry, including health care facilities, education, transportation, special revenues and pollution control, the Fund will be more susceptible to associated risks and developments. </td></tr> <tr style="page-break-inside:avoid"> <td style="line-height:0pt;padding-left:0pt;padding-right:2pt;text-align:left;vertical-align:top;width:3.80%">  </td> <td style="color:#000000;font-family:Arial;font-size:9pt;font-style:Normal;font-weight:Normal;line-height:12pt;padding-left:2pt;text-align:left;text-decoration:none;text-transform:none;vertical-align:top;width:96.20%">The Fund invested in below investment grade (high yield) municipal securities. Debt securities rated below investment grade are commonly referred to as “junk bonds” and are considered speculative with respect to the issuer’s capacity to pay interest and repay principal. These securities involve greater risk of loss, are subject to greater price volatility, and may be less liquid and more difficult to value, especially during periods of economic uncertainty or change, than higher rated debt securities. </td></tr> <tr style="page-break-inside:avoid"> <td style="line-height:0pt;padding-left:0pt;padding-right:2pt;text-align:left;vertical-align:top;width:3.80%">  </td> <td style="color:#000000;font-family:Arial;font-size:9pt;font-style:Normal;font-weight:Normal;line-height:12pt;padding-left:2pt;text-align:left;text-decoration:none;text-transform:none;vertical-align:top;width:96.20%">The market prices of the Fund’s fixed income securities may fluctuate significantly when interest rates change. The value of your investment will generally go down when interest rates rise. A rise in rates tends to have a greater impact on the prices of longer term or duration securities. For example, if interest rates increase by 1%, the value of a Fund’s portfolio with a portfolio duration of ten years would be expected to decrease by 10%, all other things being equal. A general rise in interest rates could adversely affect the price and liquidity of fixed income securities. The maturity of a security may be significantly longer than its effective duration. A security’s maturity and other features may be more relevant than its effective duration in determining the security’s sensitivity to other factors affecting the issuer or markets generally, such as changes in credit quality or in the yield premium that the market may establish for certain types of securities (sometimes called “credit spread”). In general, the longer its maturity the more a security may be susceptible to these factors. When the credit spread for a fixed income security goes up, or “widens”, the value of the security will generally go down. </td></tr> <tr style="page-break-inside:avoid"> <td style="line-height:0pt;padding-bottom:0pt;padding-left:0pt;padding-right:2pt;text-align:left;vertical-align:top;width:3.80%">  </td> <td style="color:#000000;font-family:Arial;font-size:9pt;font-style:Normal;font-weight:Normal;line-height:12pt;padding-bottom:0pt;padding-left:2pt;text-align:left;text-decoration:none;text-transform:none;vertical-align:top; width:96.20%">If an issuer or guarantor of a security held by the Fund or a counterparty to a financial contract with the Fund defaults on its obligation to pay principal and/or interest, has its credit rating downgraded or is perceived to be less creditworthy, or the credit quality </td></tr></table> <table cellpadding="7" cellspacing="0" style="text-align:start; border-collapse:collapse;empty-cells:show;margin-top:0pt;width:100%"> <tr style="page-break-inside:avoid"> <td style="line-height:0pt;padding-left:0pt;padding-right:2pt;text-align:left;vertical-align:top;width:3.80%">  </td> <td style="color:#000000;font-family:Arial;font-size:9pt;font-style:Normal;font-weight:Normal;line-height:12pt;padding-left:2pt;text-align:left;text-decoration:none;text-transform:none;vertical-align:top;width:96.20%">or value of any underlying assets declines, the value of your investment will typically decline. Changes in actual or perceived creditworthiness may occur quickly. The Fund could be delayed or hindered in its enforcement of rights against an issuer, guarantor or counterparty. </td></tr></table> 1000000000 common stock 22771349 22771349 The Fund is in the process of liquidating its assets pursuant to the Plan of Liquidation and Dissolution approved by stockholders at a meeting held on July 17, 2025 (see Notes to Financial Statements, Note 8).