Background: Oxygen free radicals play an important role in the reperfusion injury and in the deleterious effects of cardiopulmonary bypass (CPB). Iron-catalyzed formation of hydroxyl radicals has been postulated to occur during reperfusion of ischemic tissues. Recent evidence suggests that post ischemic myocardial dysfunction "stunning" is mediated by iron-catalyzed free radical reactions. To assess the role of iron-catalyzed oxidant production in ischemia-reperfusion injury to the myocardial muscle in patients undergoing elective CABG, we examined the effects of infusing an iron chelator deferoxamine after induction of anesthesia on oxidative stress reflected on the extent of lipid peroxidation and cardiac enzyme release and on myocardial performance.Material and methods: forty patients undergoing elective on-pump CABG with ejection fraction>40% were randomly divided into two groups. The deferoxamine group (n=20) received deferoxamine infusion immediately after induction of anesthesia 30mg/kg dissolved in 250ml NS 0.9% for four hours, while the control group (n=20) received 250ml NS 0.9% infusion as placebo. Haemodynamic monitoring and measurement of lipid peroxidation (by measuring malondialdehyde (MDA) were carried out before, during and after bypass. Left ventricular ejection fraction (EF) and wall motion score index (WMSI) were measured before and one hour after emerging from by pass using TEE.Results: There was highly significant decrease in the oxidative stress and lipid peroxidation in the deferoxamine group measured by MDA (P value = 0.003 during bypass and P value = 0.0001 one hour after bypass) and decreased in troponin I release (P value 0.0001). There was also negative correlation between the decrease in MDA measurement and the increase in the EF. Conclusion In patients undergoing CABG, deferoxamine infusion ameliorates oxygen free radical production and protects the myocardium against reperfusion injury.