Abstract: Objective To study the relation of cardiac function and myocardial infarction size, which is induced by different occlusion time course of left anterior descending (LAD) in rats. Methods Myocardial infarction was induced by LAD occlusion in male Wistar rats. There is 60 male Wistar rats were randomly divided into six groups: acute LAD occlusion (15，30，45 or 60 min) with reperfusion or permanent LAD occlusion group. 4 weeks after different LAD ligation treatment, pathological morphology, IS and mortality was be detected and analyzed. And 1 month Afler LAD occlusion, we used multipurpose polygraph to measure heart rate(HR), left ventricular systolic pressure (LVSP), left ventricular end-diastolic pres sure (LVEDP), 士 dp/dt_max，artery systolic pressure(ASP), artery diastolic pressure(ADP). Results The myocardial necrosis or infarction was formed by LAD occlusion for at least 30 minutes. Almost the same infarct area had formed in rats among occlusion (45 or 60 min) with reperfusion groups, or permanent occlusion group. However, when arterial blood flow was restored (occlusion with reperfusion), the scattered bleeding and cell damage in rat myocardial infarction area occurred. After permanent LAD occlusion or occlusion reperfusion, nearly 25% rats died of ventricular fibrillation within 4 hours, and most of them died within the first 30 minutes. The heart sections from rats of one month after LAD occlusion showed the typical acute myocardial infarction pathological morphology. Compared to the LAD occlusion (15 or 30 min) with reperfusion group, ASP, LVSP and 土 dp/dt_max of the LAD occlusion(45 or 60 min) with reperfusion or permanent LAD occlusion group were decreased, LVEDP increased. Conclusion The rat acute myocardial infarction model is the most stable by LAD occlusion (at least 45 minutes) with reperfusion and the change of cardiac function is related with the size of myocardial infarction areas after LAD occlusion with reperfusion.