To evaluate the safety and efficacy of tirofiban, a specific inhibitor of the platelet glycoprotein Ⅱ b/Ⅲa receptor, in the treatment of unstable angina and myocardial infarction without persistent ST elevation (acute coronary syndrome, ACS), a total of 200 patients were randomly assigned to a heparin group and a tirofiban+heparin group on double-blind basis and the treatment effects of the two protocols on ACS were compared when the patients of both groups were taking aspirin at the same time. The composite primary end-point events consisted of death, myocardial infarction, or refractory ischemia. Our results showed that the frequency of the composite primary end point events in 30 days was lower in tirofiban+heparin group as compared with that of heparin group (13.9% vs 29.3%, P=0.010). The rates of the other composite end point events in the tirofiban+heparin group were also lower than those in the heparin group in 4.5 days and in 30 days. Bleeding complication occurred in 7.0% of the patients receiving heparin alone and in 12.7% of the patients receiving tirofiban and heparin in combination (P=0.1717).The study showed that the incidence of ischemic events in patients with ACS receiving tirofiban+heparin was lower when compared with that of patients who received only heparin and aspirin, suggesting that tirofiban might be of special value in the treatment of ACS.