Objectives: To evaluate the effect of urapidil on myocardial perfusion, and ventricular function in patients with ST-elevation acute coronary syndrome (ACS) treated with primary percutaneous coronary intervention (PCI).Methods: Fifty-four patients were randomized into urapidil (12.5mg, ic, n=27) or control group. Infarct related artery (IRA) was targeted with PCI following urapidil administration. TIMI blood flow, corrected TIMI frame count (cTFC), myocardial blush grade (MBG), ST resolution (STR) on ECG, creatine kinase MB (CK-MB) and cardiac troponin T (cTnT) were measured before, and after PCI.Results: cTFC (18.38±3.30 vs. 21.44±4.26, P=0.005), in the treatment group was lower than the placebo group, whereas MBG was higher (P=0.04). More patients in the urapidil group achieved significant STR following PCI (93% vs. 70%, P=0.04). Left ventricular ejection fraction (LVEF), measured with echocardiography, in the urapidil group was higher than the control group 30 days after PCI (0.58±0.06 vs 0.54±0.06, P'0.04). Peak CK-MB and peak cTnT in the urapidil group was lower than the control group (P<0.01). Myocardial nitric oxide concentration in the urapidil group was higher than that of the control group (P<0.01). Following PCI, the endothlin-1 level did not change in the urapidil group (P>0.05) but it was increased in the control group (P<0.05).Conclusions: Urapidil treatment improves coronary flow, myocardial perfusion and left ventricular function following PCI in patients with ST-elevation ACS. These beneficial effects are associated with an enhanced biosynthesis of nitric oxide.