In this retrospective cohort study, 36 consecutive patients at a single center in Iran with HER-2 positive breast cancer with asymptomatic mild LVSD with LVEF 40–53% without heart failure symptoms and those who were closely followed in the Cardio-Oncology clinic before initiating the treatment and then every two cycles of trastuzumab were included. This evidence concerns the gene ERBB2 and breast carcinoma.