Background: Another option to intravenous (IV) trastuzumab is subcutaneous (S.C.) trastuzumab, which has received approval. There is a lack of information regarding the causes and prevalence of cardiotoxicity in patients treated with subcutaneous versus intravenous trastuzumab for early-stage of HER2-positive breast cancer. Objectives: To compare cardiotoxic effects of IV versus SC trastuzumab. Patients and methods: This retrospective study included 187 patients with HER2+ breast cancer treated with adjuvant trastuzumab (either IV or SC) for at least 6 months, stage (I, II, III), with initial ejection fraction (EF) (≥ 55 %) and followed up at least 2 times with echocardiographyduring treatment. We compared patients who received IV (88 patients) versus SC (99 patients) trastuzumab as regard patients and disease characteristics, treatment received, cardiotoxicity development and its pattern, treatment discontinuation, progression status, and its pattern.Analysisofdifferent variables to identify predictors of trastuzumab induced cardiotoxicity in both groups was done. Results: The overall incidence of trastuzumab induced cardiotoxicity was 16.6%. By comparing both groups, there was no significant difference as regard patients, disease characteristics, cardiotoxicity and treatment received except for number of anthracycline cycles. There were no detected risk factors for cardiotoxicity in both groups except number of anthracycline cycles. Conclusion: There was no significant variance in cardiotoxicity between both groups. Both the IV and SC formulas of trastuzumab had equivalent safety profiles in our study. When deciding between these formulations, other factors—such as patient preference, value to patients and the healthcare system, and cost—might also be taken into account.