Objective To explore effects of 17β-estradiol preconditioning on myocardial ischemia-reperfusion(I/R) injury of rats and its mechanism. Methods Totally 30 female SD rats were ovariectomized and divided randomly into C group (sham), I/R group and I/R+ESUB>2 /SUB>group (17β-estradiol pretreatment). After 2 weeks of pretreatment with 17β-estradiol, all rats were subjected to the left anterior descending coronary occlusion for 30 minutes and reperfusion for 2 hours. The sizes of myocardial infarction area were measured by triphenyltetrazolium chloride (TTC) staining; the apoptotic rate was assayed by flow cytometer, the protein expression of EM>c-fos/EM> proto-oncogene in cardiomyocytes was detected by semiquantitative immunohistochemical technique. Results 17β-estradiol significantly attenuated the infarct size of myocardium injured by ischemia-reperfusion, decreased the apoptotic rate in cardiomyocytes, also inhibited the expression of c-Fos protein in cardiomyocytes.Conclusion These results suggest that estrogen protects the heart against ischemia-reperfusion injury of rat，its cardioprotective mechanism