Background To evaluate the efficacy and short term prognosis of tirofiban in different treatment duration in patients with acute ST segment elevation myocardial infarction (STEMI) and percutaneous coronary intervention (PCI)combined with intracoronary injection.Methods A total of 125 patients with acute STEMI were enrolled in the trial.They were randomly divided into 2groups: tirofiban group (n=64) and control group (n=61).The tirofiban was used by intracoronary and intravenous application in tirofiban group which was randomly divided into 3 sub-groups again according to the duration of tirofiban by persistent intravenous injection for 12 hours, 24 hours or 36 hours.Thrombolysis in myocardial infarction flow (TIMI flow) and myocardial perfusion grades were recorded immediately after PCI.The adverse cardiac events and cardiac death within 180 days of PCI, and the adverse effects (hemorrhage and thrombocypenia) were compared between the 2groups and within tirofiban sub-groups.