Treatment with trastuzumab in Human Epidermal Growth Factor Receptor 2 (HER2)-positive breast cancer (BC) has dramatically changed the prognosis of early disease, reducing the risk of recurrence by 40% and risk of death by 34%.1 Clinically, the most significant adverse reaction to anti-HER2 treatment is cardiotoxicity, which is manifested most often as asymptomatic reduction in left ventricular ejection fraction (LVEF), though a minor subset of patients experience overt congestive heart failure (CHF) and, very rarely, cardiac death.2 This evidence concerns the gene ERBB2 and breast cancer.