Trastuzumab combined to chemotherapy had demonstrated significant improvement of time to progression and survival in metastatic breast cancer patient overexpressing HER-2. Cardiac toxicity was an unexpected side effect. The incidence of cardiac dysfunction was dependent on prior or current anthracycline exposure. The mechanism of action involved for this cardiac toxicity is unclear. We discuss in this article the incidence, the physiopathology, the risk factors, the predictive factors and the patient management and on cardiotoxicity of trastuzumab.