Abstract
Trastuzumab (TZ), a monoclonal antibody against human epidermal growth factor receptor type 2 (HER2), is an important biological agent used for the treatment of positive breast cancer. This paper presents a 46-year-old female patient who developed right heart failure and right ventricular dysfunction while on TZ due to breast cancer, and returned to normal following the discontinuation of the drug. As far as we know, this is the first case report related to a patient presenting with right ventricular dysfunction and induced cardiotoxicity while on TZ.