Based on the indispensable role of NRG-1/ErbB system in the heart and the analogy between ErbB2 knockout-induced cardiomyopathy and trastuzumab-induced heart failure, many have concluded that trastuzumab causes cardiotoxicity by blocking the physiological actions of ErbB2 in the heart [88]. The gene discussed is ERBB2; the disease is heart failure.