Abstract: Objective: To investigate the effects of NO on cardiomyocyte injuries in myocardial stunning caused by the recurrent, reversibl emyocardial ischemia reperfusion injury Methods: New Zealand white rabbits were anesthetized with intravenous pentobarbital A suture ligature was passed around the left anterior descending coronary artery（LAD), so it could be snare occluded and reperfused The LAD was occluded for 10min three times, the first and second occlusions were followed by 10min of reflow, after the third occlusion, the reperfusion was 120min Fifteen rabbits were randomly divided into three groups: 1 control group n=5.2.L-Arg group n=5 3.L-NNA group n=5 The contents of NO in the blood were measured by ESR and the dp/dtmax we re recorded The myocardial tissues were obtained for the observation of cardiomyocyte injuries with electron microscopy Results: Compared with control group,in.L-Arg group, the contents of NO increased markedly and dp/dt max decreased markedly,the cardiomyocyte seemed to have more severe magnifications of cardiomyocyte injury: some of sarcomeres became blurred, the number of swelled mitochondria increased But in.L-NNA group: the contents of NO decreased markedly, the decreased dp/dt max and the number of the swelled mitochondri a were less than that in control group, there were no blurred sarcomeres Conclusion: NO might have a harmful effect on cardiomyocyte injury in myocardial stunning