Background: HER2 or is a member of the epidermal growth factor family which if expressed, accounts for extremely aggressive breast cancer. HER2 regulates signaling (Raf/Ras/MAPK and PI3K/AKT) through several pathways associated with cell survival. However, Trastuzumab, an inhibitor of this has shown promising results in patients with HER 2 positive expressions. Though, trastuzumab is well tolerated, some patients report with cardiotoxicity. This may be attributed to mutations or polymorphisms of HER2 gene. Objectives: The aim of our present study is to find out whether HER2 gene polymorphisms, I655V and A1170P are associated with the drug related cardiotoxicity, to correlate SNPs with the LVEF at 3 month and 6-month interval of time Methodology: Seventy-two patients with carcinoma breast who were eligible for trastuzumab monotherapy were recruited in the study. Genomic DNA will be performed using phenol-chloroform method with PCR-RFLP method. Assessment of cardiac function will be done on every follow up. Cardiac function primary and secondary outcomes will be recorded.