Myo-inositol hexaphosphate (phytic acid), a highly charged antioxidant, has been found to chelate metal ions such as iron and calcium and to scavenge hydroxyl radicals, .OH. This study examined the efficacy of this antioxidant and redox agent in attenuating myocardial reperfusion injury. Sprague-Dawley rats were injected intravenously with three different doses of phytic acid (group 1, saline solution only, control; group 2, 1.5 mg/100 g; group 3, 7.5 mg/100 g; group 4, 15 mg/100 g) 30 minutes before excision of hearts. Isolated hearts were prepared by the Langendorff technique. Global ischemia was induced for 30 minutes, followed by 30 minutes of reperfusion. As expected, in group 1, reperfusion was associated with enhanced creatine kinase release, reduced coronary flow, poor recovery of ventricular function as evidenced by reduced left ventricular developed pressure and the first derivative of left ventricular pressure, and increased lipid peroxidation. Groups 3 and 4, but not group 2, demonstrated myocardial protection as evidenced by reduced creatine kinase release, improved left ventricular function and coronary flow, and decreased lipid peroxidation compared with the control group. These results suggest that potential use of this antioxidant in salvaging the heart from ischemic and reperfusion injury.