Doxorubicin (DOX) is the most effective chemotherapeutic for breast cancer, but it is usually associated with severe cardiotoxicity. Further investigation to alleviate its side effects is essential. The present study investigated the mechanism of the cross-organ communication between tumors and the heart and potential intervention targets. Morphological bubble-like protrusions were observed in both adult murine ventricular cardiomyocytes (AMVCs) and human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) cocultured with breast cancer cells (BCCs), along with elevated expression of pyroptosis-related proteins. Exosomes (EXOs) from DOX-treated BCCs aggravated DOX-induced cardiotoxicity (DOXIC) in an orthotopic mouse model of breast cancer. Blocking miRNAs by knocking down Rab27a or inhibiting the release of EXOs in cancer tissue by Dicer enzyme knockout attenuated this additional injury effect. Exosomal miRNA sequencing revealed that miR-216a-5p is especially upregulated in EXOs from DOX-induced BCCs. Mechanistically, miR-216a-5p was upregulated by enhanced transcription mediated by DOX-induced AMP-dependent transcription factor 3 (ATF3) and packaged into EXOs by splicing factor 3b subunit 4 (SF3B4) in BCCs. Itchy E3 ubiquitin-protein ligase (ITCH) was identified as a novel downstream target mRNA of miR-216a-5p. ITCH negatively mediated thioredoxin-interacting protein (TXNIP) ubiquitination to activate the NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome pathway, ultimately leading to cardiomyocyte pyroptosis. Our findings revealed novel cross-organ pathogenic communication between breast cancer and the heart through the exosomal miR-216a-5p-mediated ITCH/TXNIP/NLRP3 pathway, which drives cardiomyocyte pyroptosis. These findings suggest that targeting myocardial miR-216a-5p or blocking harmful EXOs from breast cancer is a potential therapeutic strategy for alleviating DOXIC.