Objective:To develop a new method of measuring infarct size by staining hearts in vivo after ischemia-reperfusion,and compare with the traditional method of staining in vitro to determine its feasibility. Methods:Adult male Sprague-Dawley rats were subjected to 30 min myocardial ischemia and 6 h reperfusion by ligation of the left anterior descending coronary artery. Cardiac function was evaluated by echocardiography and serum creatine kinase(CK) activity was also measured by a biochemical analyzer. After reperfusion for 24 h,hearts were staining by triphenyltetrazolium chloride(TTC)-Evans blue in vitro or in vivo. Infarct area(IA)/ risk area (RA) was calculated. Finally we compared the success rate of the two methods,and made correlation analysis of the IA/RA with serum CK activity. Results:There was no significant difference in IA/RA staining by the two different methods. However,success rate of staining in vivo was significant higher than that of staining in vitro. Besides,compared with staining in vitro,there was a stronger correlation between IA/RA and CK activity by staining in vivo. Conclusion:The method of staining in vivo is much easier to operate,and it can evaluate the damage by myocardial ischemia-reperfusion injury more accurately than that of staining in vitro.