Aim To investigate the effect of tirofiban on coronary flow and microcirculation in patients with ST segment elevation myocardial infarction(STEMI) treated by primary percutaneous coronary intervention(PCI).Methods 58 patients with primary STEMI who underwent primary PCI were randomized to receive either tirofiban and primary PCI(n= 30) or primary PCI alone(n= 28).Baseline characteristics of the two groups were compared.The patency rate of infarct-related artery(IRA) before intervention,the flow of thrombolysis in myocardial infarction(TIMI) before and after surgery,the resolution of ST segment,endothelial cell apoptosis,blood coagulation factor,the incidence of bleeding complications and acute ischemic events during hospitalization as well as the left ventricular ejection fraction(LVEF) measured by echocardiography before discharge were studided.Results A greater percentage of TIMI 1 flow was achieved in the tirofiban group(p< 0.05).On the other hand,TIMI 0 flow was more commonly found in patients of the control group(p< 0.01).There was no difference between the two groups in percentage of TIMI 2 and 3 flow achieved in IRA after PCI(p> 0.05).The no-reflow phenomena,reperfusion arrhythmia,endothelial cell apoptosis,blood coagulation factor were less in the tirofiban group(p< 0.05),and faster ST segment resolution in the tirofiban group after PCI(p< 0.05).There was no significant difference between the two groups in occurrence of major adverse cardiovascular events(MACE) or bleeding in both groups.Conclusions Tirofiban treatment can improve the rates of recanalizationand and the TIMI flow to the acute myocardial infarction with PCI,the surgery can be done better.It can avoid more myocardial cell to die permanently,and improve microcirculation disfunction.