Objective To investigate the effect of total flavonoid of Herba Pyrolae(TFHP) on the changes of ECG in rats with acute myocardial ischemia as well as the mechanism of the action.Methods Acute myocardial ischemic model was established by intravenous injection of pituitrin in rats,and ECG was recorded.Acute myocardial infarction model was established by the ligation of left descending coronary artery in rats,and serum level of nitric oxide(NO) and free fatty acid(FFA) was determined with spectrophotometrical method besides ECG.Results In comparison with the model controls,TFHP antagonized the decreased T wave by pituitrin and ligating coronary artery,and increased NO level and reduced FFA concentration in the serum of rats with acute myocardial ischemia.Conclusion TFHP protects the myocardium from ischemic injury possibly through increasing NO release and decreasing FFA production.