Antibody-drug conjugates (ADCs), such as trastuzumab emtansine and trastuzumab deruxtecan, are effective in treating erb-b2 receptor tyrosine kinase 2 (ERBB2)–positive breast cancer (BC) that has progressed on prior ERBB2-targeted therapy, warranting evaluation of their cardiotoxic profiles. Here, ERBB2 is linked to breast cancer.