Trastuzumab, an antibody targeting the Human epidermal growth factor 2 receptor (HER/ErbB2), and used as first choice therapy against breast cancer (13, 14), also inhibits this receptor in cardiomyocytes, affecting myocardial structure and survival pathways, triggering cardiomyocyte apoptosis and leading to asymptomatic decreased left ventricular ejection fraction, and eventually heart failure, particularly when it is used in combination with other agents, such as anthracyclines (15, 16). The gene discussed is ERBB2; the disease is heart failure.