This multicenter, randomized clinical trial will include 112 patients treated by adjuvant trastuzumab for HER2 positive breast cancer to investigate the effects of a 3 months’ supervised exercise program (intermittent exercise, combining moderate and high intensities; 55 minutes duration, 3 times per week), on the rate of cardiotoxicity [defined by either a decrease of the LVEF under 50% or an absolute drop of LVEF of 10%] between baseline and at 3 months and on strength, aerobic capacity, metabolic, inflammatory and hormonal parameters. The gene discussed is ERBB2; the disease is breast cancer.