Abstract: Objective To investigate the curative effect and the security of applying tirofiban before primary percutaneous coronary intervention (PCI) in patients with ST segment elevation myocardial infarction (STEMI) suffering no/slow reflow phenomenon. Methods A total of 296 patients with STEMI were selected into this study. All patients underwent primary PCI and applied tirofiban by intravenous route. According to the different mediction time of the tirofiban， all patients were divided into preoperative treatment group and intraoperative treatment group.  Blood flow condition of the infarction related artery (IRA) of preoperation and postoperation， postoperative left ventricular ejection fraction (LVEF)， the incidence of major adverse cardiovascular events (MACE) bleeding and serious thrombopenia (PLT<10×109/L)  during hospitalization were analysed in both groups. Results The ratio of TIMI 3 of IRA in preoperative treatment group was significantly higher than those of intraoperative treatment group in preoperation (74.7% vs 47.2%，P<0.05) and postoperation (98.9% vs 93.2%，P<0.05). The postoperative left ventricular ejection fraction was significantly higher in preoperative treatment group than in intraoperative treatment group (58.31±5.35)%  vs  (52.93±6.01)%(P<0.05). There were no significant difference in the incidence of MACE， bleeding and serious thrombopenia during hospitalization in both groups. Conclusion Preoperative tirofiban treatment can reduce the incidence of no and slow reflow phenomenon and protect the heart function， additionally， preoperative tirofiban does not increase the incidence of postoperative bleeding in patients with STEMI.

Key words: myocardial infarction；angioplasty, balloon, coronary；noreflow , phenomenon