Objective:To investigate the expression of cyclin A2 in rat cardiac myocytes after acute myocardial infarction(AMI). Methods:The total 30 adult male SD rats were randomly divided into 6 groups averagely,sham-operated group and other 5 AMI groups,3d,1w,2w,3w and 4w after AMI. The expressions of cyclin A2 and phospho-histone H3(H3P) were detected by immunohistochemistry in each group. Results:Compared with sham-operated group,the number of cyclin A2 positive myocytes increased remarkably after AMI,but decreased 2 weeks later gradually. And after 4 weeks after AMI,there was no difference in cyclin A2 expression in heart tissue between AMI group and the sham-operated group. In each group H3P expression increased remarkably at 3d,1w,2w,3w after AMI in nucleus of some myocytes. The positive expression rate of H3P was 1.56% to 3.12% in heart tissue after AMI. Conclusion:The expression of cyclin A2 and H3P indicates that some adult cardiac myocytes can reenter cell cycle after AMI.