Objective To explore the role of NADPH oxidase inhibitor apocynin on ischemia/reperfusion (I/R)-induced myocardial injury.Methods Male SD rat hearts were divided into the normal control group; sham group; I/R group (1 h ischemia followed by 3 h reperfusion) ; I/R + apocynin group (50 mg/kg,administrated at 30 min before reperfusion) and I/R + vehicle group (same volume vehicle administrated at 30 min before reperfusion).At the end of reperfusion,myocardial infarct size,apoptosis,plasma CK activity,myocardial NOX activity,myocardial caspase-3 expression and activity,myocardial mRNA and protein expressions of vascular peroxidase 1 (VPO1) and NOX2 were measured.Results Infarct size,ratio of cardiomyocyte apoptosis,mRNA and protein expression of VOP1 and NOX2,serum CK,myocardial NOX and caspase-3 activities in the I/R group were all significantly increased compared to those in the sham group (P ＜0.01).Above parameters were similar between I/R + vehicle group and I/R group (all P ＞ 0.05).Infarct size,ratio of cardiomyocyte apoptosis,myocardial mRNA and protein expression of VOP1 and NOX2,serum CK,myocardial NOX and caspase-3 activities were significantly lower in I/R + apocynin group compared to those in I/R group (all P ＜ 0.01).Conclusions NOX/VPO pathway plays an important role in mediating I/R-induced myocardial oxidative injury.NOX inhibition could reduce I/R-induced myocardial oxidative injury by attenuating myocardial apoptosis in this model.