BACKGROUND: Glucose-insulin-potassium (GIK) may improve cardiovascular performance after coronary artery bypass graft surgery (CABG). Our study investigated whether an infusion of GIK during elective CABG surgery in type II diabetic patient improved left ventricular performance. METHODS: We measured left ventricular ejection fraction and troponin (Tn), a myofibrillar structural protein. In this research, after ethics committee approval, 50 patients with type 2 diabetes mellitus (DM) were enrolled into a randomized simple sampling, prospective, double-blind clinical trial study. In the case group, 500 cc dextrose water 5% plus 80 IU regular insulin and 40 mEq KCL were infused at the rate of 30 cc/hr. Patients in control group received 5% dextrose solution at the rate of 30cc/hr. Venous blood samples were taken before induction of anesthesia, after removal of the aortic clamp and before discharging from hospital. The Mann-Whitney-test was used to test for differences in Tn concentration between the groups. Fisher’s exact test was used to determine whether there was a difference in the proportion of patients with a low ejection fraction (<45%) in the case group compared with that in the control group. Changes in potassium and glucose concentrations over time within the groups were examined by ANOVA and paired t-tests. P<0.05 was regarded as significant level for all tests. RESULTS: In this study, 50 patients with type 2 DM were evaluated in case and control groups. The mean age ± SD in the case group was 57.7 ±9.9 years and in the other group was 61.2 ± 8.4 years. The groups were well-matched for age, sex and number of bypass grafts. Randomization did not give an equal distribution of male and female patients. There wasn’t any significant difference in ejection fraction between the case and control groups before and after CABG (P>0.05). Tn concentration in the case group was 3.3 ± 5.0 and in the control group was 3.9 ± 5.1. There was no significant difference in Tn between the two groups before and after CABG (P>0.05). There was not any significant difference in hospitalization time between the two groups. CONCLUSION: The results suggested that GIK can’t improve left ventricular performance in routine CABG surgery. Keywords: Cardiovascular surgery, Glucose-Insulin-Potassium, Cardiac troponin.