Abstract: Objective:To investigate the protective effects of ethanol postconditioning on isolated rats' hearts, and discuss the antioxidative mechanism. Methods:Hearts isolated from male Sprague-Dawley rats were perfused on a langendorff apparatus and subjected to 30 minutes of regional ischemia(occlusion of left anterior descending artery) followed by 120 minutes of reperfusion. The ventricular hemodynamic parameters were measured. SOD activity and MDA content were detected to evaluate cell antioxidant ability. The expressions of aldehyde dehydrogenase 2,Bcl-2 and Bax at mRNA level of left anterior myocardium were detected by RT-PCR analysis. Results:Compared with ischemia-reperfusion group, ethanol postconditioning improved the recovery of left ventricular developed pressure,maximal rise/fall rate of left ventricular pressure(P<0.01),SOD activity was increased and the content of MDA was decreased,Bcl-2 mRNA expression was increased,while Bax mRNA expression was decreased. Administration of ALDH2 inhibitor CYA attenuated the effect of ethanol postconditioning,the recovery of hemodynamic parameters were inhibited(P<0.01),SOD activity was decreased and the content of MDA was increased,Bcl-2 mRNA expression was decreased,Bax mRNA expression was increased. Conclusions:The protective effect of ethanol postconditioning on isolated rats' hearts is related to upregulating mitochondrial ALDH2 mRNA expression,likely through its antioxidative role and reduction of myocardial apoptosis.