Giving preoperative loading dose of 60mg of trimetazidine can safely and effectively reduce the PCI-related myocardial damage for the patients undergoing selective PCI. but the effect of Trimetazidine during the primary PCI on cardiac function in patients with ST-elevation myocardial infarction is not sure. this study aim to study the effect of Trimetazidine during the primary PCI on cardiac function in patients with ST-elevation myocardial infarction.