Background Aspirin and clopidogrel can improve myocardial reperfusion and alleviate myocardial injury during percutaneous coronary intervention (PCI).Whether the addition of intravenous tirofiban during this procedure produces further benefit has not been clarified in ST segment elevation myocardial infarction(STEMI)patients.We evaluated this on STEMI patients who underwent primary PCI(p-PCI)via transradial artery approach.Methods Consecutive patients were randomized into tirofiban group(n=72)or placebo group(n=78).Angiographic analysis included initial and final thrombolysis in myocardial infarction(TIMI)flow grade(TFG),corrected TIMI frame count(CTFC)and TIMI myocardial perfusion grade(TMPG)of the thrombotic vessel.Platelet aggregation rate(PAR),creatine phosphokinase(CPK),CPK isoenzyme MB(CPK-MB)and troponin I levels were measured and TIMI definitions were used to assess bleeding complications.Left ventricular performance parameters were investigated with equilibrium radionuclide ventrjculography.Major adverse cardiac events(MACE)were followed up for 6 months.Results The cases of TFG 0 and 1 before PCI,TFG 0 when first crossing of guide wire were less,and the cases of TFG 3 after PCI was more in tirofiban group than those in placebo group.The final CTFC was fewer and the incidence of no reflow phenomenon was lower,as well the percentage of final TFG 3 was higher in tirofiban group than those in placebo group (all P＜0.05).Mean peak CPK-MB was significantly lower,while the left ventricular performance parameters 1 week after PCI were much more improved in tirofiban group than those in the placebo group.PAR was significantly decreased shortly after tirofiban infusion.The incidence of 6-month MACE in tirofiban group was obviously lower than that in the placebo group.No statistical difference was noted between the two groups with regard to bleeding complications.Conclusions Intravenous tirofiban infusion,in addition to aspirin and clopidogrel in STEMI patients with P-PCI via transradial artery access,can quickly inhibit platelet aggregation,loosen occlusive thrombus,improve myocardial reperfusion and reduce incidence of MACE with few complications of vessel access and bleeding.