Studies using ErbB2 mutant mice have shown that the following cardiac toxicity phenotypes are observed: 1 thinning of the ventricular wall, reduced LVEF, fibrosis, and increased myocardial cell apoptosis, leading to dilated cardiomyopathy (DCM) and death from heart failure within a few months [13] and 2 progressive cardiac enlargement and reduced contractile function (LVEF < 40%), myocardial sarcomere structure breakdown, Z-line disorganization, increased cell death, and cardiac structural abnormalities due to fibroblast infiltration and interstitial fibrosis [14], among others. Here, ERBB2 is linked to heart failure.