Abstract: AIM:To study the effect of glucose-insulin-potassium (GIK) on changes of dog myocardial cells after ischemia-reperfusion injury following acute myocardial ischemia/reperfusion (MI/R) and to explore the role of insulin in the protective effects of GIK on myocardium. METHODS: In anesthetized open-chest dogs, the left anterior descending coronary artery (LAD) was partially occluded (80% reduction in its blood flow) for 50 min and reperfused for 4 h. Dogs were randomly divided into three groups: GIK, GK and saline. All treatments began at 5 min before reperfusion ［infused at 2 ml/(kg·h), i.v.］ and continued during the 4-h reperfusion. The ratio of necrosis area was determined. Myocardial infarction was determined by the ultrastructure of ischemic myocardium at the end of the reperfusion. RESULTS: The ratio of myocardial necrosis showed attenuation in GIK group ［(5.2±0.8)% vs. saline (9.4±0.8)%, P<0.05］, but no reduction was observed in myocardial infarct size in the GK group ［(8.5±0.9)% vs. saline (9.4±0.8)%］. Compared with saline, GK had no significant effects on the ultrastructure of ischemic myocardium, whereas GIK had significant effects on the ultrastructure of ischemic myocardium. CONCLUSION: GIK exerts some protective effects on myocardium by alleviating ultrastructural injury of myocardium. Insulin may play a leading role in the actions of GIK.