Objective:To observe the effect of naloxone(Nal) on cardiomyocyte apoptosis and expression of Fas and FasL following acute ischemia-reperfusion injury in vivo and to explore its mechanism. Methods:Twenty-four SD rats were selected and randomly divided into three groups:sham-operated group(sham group), ischemia-reperfusion group(IR group),IR and treated with naloxone group(Nal group). Terminal deoxynucleotidyl transferase mediated dUTP nick end labeling(TUNEL) and Western blotting were used respectively to detect the cardiomyocyte apoptosis and protein expressin of Fas and FasL, and histopathological changes of myocardium were observed by optic microscopy. Results:Numerous apoptotic cardiomyocytes were found and the expression of Fas and FasL were increased significantly in ischemic fields in the IR group as compared to sham group(P < 0.01), apoptosis and the expression of Fas and FasL were decreased significantly in the Nal group as compared with IR group(P < 0.01). Local myocytes lesions were observed in myocardium in the IR group, but the injury was lessened significantly in the Nal group. Conclusion:The expression of Fas and FasL in ischemia-reperfusion myocardium can induce cardiomyocyte apoptosis, and naloxone has the cardioprotective effects in ischemia-reperfusion injury by significantly inhibiting the cardiomyocyte apoptosis induced by Fas and FasL expression.