[Objective] To investigate the efficacy and safety of trastuzumab in the treatment of human epidermal growth factor receptor 2(HER2) positive metastatic breast cancer. [Methods] The clinical efficacy and side effects of trastuzumab plus chemotherapy in the first-line treatment of 66 patients with HER2-positive metastatic breast cancer were analyzed retrospectively. Cardiac function changes in left ventricular ejection fraction(LVEF) were monitored by color echocardiography.[Results] Three patients had compl...