Aim To study the effects of late reperfusion on cardiocyte apoptosis and the expression of bcl-2 and bax mRNA and related proteins in the risk areas after acute myocardial infarct in dogs. Methods After chest was opened and the coronary artery was exposed,twenty eight dogs were randomly divided into three groups: sham operation group(n=8),acute myocardial infarction group(n=10),and late reperfusion group(n=10).Apart from sham operation group,the left anterior descending arteries were occluded for 12 h in acute myocardial infarction group and 6 h occlusion followed by 6 h of reperfusion in late reperfusion group.The cardiocyte apoptosis was measured by TUNEL assay,the expression of bcl-2 and bax gene mRNA by RT-PCR.Immunohistochemistry and Western blot analysis were used to detect the expression of bcl-2 and bax protein. Results The apoptotic index of cardiocyte in late reperfusion group was much higher than that of sham operation group(p<(0.01)),but less than that of acute myocardial infarction group(p<0.05).Compared with sham operation group,the expression of bcl-2 mRNA and protein were significantly increased in acute myocardial infarction group and late reperfusion group(p<(0.01)),and there were no significant difference between acute myocardial infarction group and late reperfusion group(p<0.05).The expression of bax mRNA and its protein in late reperfusion group was much higher than that of sham operation group(p<0.01), but lower than that of acute myocardial infarction group(p<0.05). Conclusions Late reperfusion of infarct-related artery can decrease cardiocyte apoptosis in the risk area of acute myocardial infarction,which may be related to the reduction of the expression of bax mRNA and protein.