Company: MYI
Filing Date: 2025-08-12
Form Type: 425
Source: 0001193125-25-178174
Chunk: 0

Company: BLACKROCK MUNIYIELD QUALITY FUND III, INC.
Filing Date: 2025-08-12
Form: 425
Chunk 0
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Filed by BlackRock MuniYield Quality Fund III, Inc. pursuant to Rule 425 under the Securities Act of 1933 and deemed filed pursuant to Rule 14a-12 under the Securities Exchange Act of 1934 Subject Company: BlackRock MuniVest Fund, Inc. Investment Company Act File No.: 811-05611 Date: August 11, 2025 Dear [Name], The BlackRock closed-endfunds listed below will be holding joint special meetings of shareholders (each, a “Joint Special Meeting”) in order to consider and vote on certain reorganizations or mergers (collectively, the “Reorganizations” and each, a “Reorganization”) among the below funds (the “Funds”), as announced on June 9, 2025 ( 6-9-2025-muni-cef-reorganization-press-release.pdf ) and as detailed below:

| • |     | BlackRock Long-Term Municipal Advantage Trust (BTA) with and into BlackRock MuniAssets Fund, Inc. (MUA) |

| • |     | BlackRock California Municipal Income Trust (BFZ) with and into BlackRock MuniHoldings California Quality Fund, 
 Inc. (MUC)                                                                                                      |

| • |     | BlackRock New York Municipal Income Trust (BNY) and BlackRock MuniHoldings New York Quality Fund, Inc (MHN) with 
 and into BlackRock MuniYield New York Quality Fund, Inc. (MYN)                                                   |

| • |     | BlackRock MuniYield Fund, Inc. (MYD), BlackRock MuniYield Quality Fund II, Inc. (MQT), BlackRock Investment                                                                                           
 Quality Municipal Trust, Inc. (BKN), BlackRock Virginia Municipal Bond Trust (BHV) and BlackRock MuniYield Pennsylvania Quality Fund (MPA) with and into BlackRock MuniYield Quality Fund, Inc. (MQY) |

| • |     | BlackRock MuniHoldings Quality Fund II, Inc. (MUE), BlackRock Municipal Income Trust (BFK), BlackRock Municipal                
 Income Quality Trust (BYM) and BlackRock Municipal Income Trust II (BLE) with and into BlackRock MuniHoldings Fund, Inc. (MHD) |

| • |     | BlackRock MuniVest Fund, Inc. (MVF), BlackRock MuniVest Fund II, Inc. (MVT) and BlackRock M