Patients undergoing multivessel off-pump coronary bypass surgery (OPCAB) inevitably experience cumulative ischemia-reperfusion injury at myocardium. Glucose-insulin-potassium (GIK) is a potentially useful adjunct to myocardial protection. This study was designed to evaluate the effects of GIK infusion on myocardium in patients undergoing OPCAB. Patients undergoing OPCAB with acute coronary syndrome are randomly assigned to GIK or Control group. The trial is double-blind and conducted at a single center.