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.