Background and Purpose: Some researchers believe that the treatment with glucose–insulin–potassium (GIK) in ST segment elevation myocardial infarction (STEMI) can reduce the mortality rate. Others, however, contradict this view. Therefore, the present study was designed to evaluate the clinical and paraclinical effects of GIK in STEMI patients.Methods: This triple blind clinical trial was conducted from September 2008 to July 2009 on 72 STEMI patients in the CCU of Vasei Hospital in Sabzevar, Iran. They were assigned through block randomization into standard care or additional GIK infusion (25% glucose, 50 IU of soluble insulin per liter, and 80 mmol of potassium chloride per liter at 1.5 ml/kg/hour). They were assessed for the number of MACEs (death, reinfarction and serious arrhythmias), plasma concentrations of cardiac enzymes (CK, CK-MB), and left ventricular ejection fraction. The statistical analysis was conducted in SPSS 11.5 using Fisher’s exact test, ttest and repeated measurement. P< 0.05 was considered as the basis of significance.Results: MACE rate was 30.3% for GIK and 25.6% for control patients (p=0.66). There was no significant difference in plasma concentrations of cardiac enzymes between GIK and control patients. Left ventricular ejection fraction was 39% for GIK and 41% for control patients (p=0.34).Conclusion: In patients with STEMI treated with streptokinase, GIK therapy offers no clinical and paraclinical effects.