In this study, we aimed to compare the myocardial protective effects of high dose ascorbic acid with the effects obtained by adding diltiazem to high dose ascorbic acid. We studied 30 elective cardiac surgery patients prospectively. In ascorbic acid group (group AA), ascorbic acid was given after induction and just before aortic declamping, 50 mg.kg-1 each time. In ascorbic acid + diltiazem group (group AA + D), diltiazem was added to ascorbic acid (0.3 mg.kg-1, i.v. after induction and then 2 micrograms.kg-1 min-1 i.v. infusion until declamping). Group C was the control group. There was no significant difference between groups in terms of cardiac enzyme levels. After declamping, the arterial and coronary sinus malondialdehyde levels, measured as a marker of lipid peroxidation, were increased significantly in the group C while remained stable in the other two groups. Ventricular fibrillation (VF) after declamping was positive in 3, 1 and 6 patients in the groups AA, AA + D and C respectively. In this study, we observed the prevention of lipid peroxidation in the group AA and group AA + D. The only positive result obtained by addition of diltiazem to high dose ascorbic acid was the decrease in the frequency of VF after declamping. We concluded that the prevention of lipid peroxidation in the groups AA and AA + D provided no measurable protection over myocardial ischaemia-reperfusion injury.