The synthetic liposoluble antioxidant BAT. 120 mg/kg, was found to produce markedly protective effects in a rat model of coronary occlusive myocardial infarction, whereas the water soluble BAT analogue, 4-Oxy-3,5-ditretbutylphenyl phosphonic acid sodiate (SFN-6), 100 mg/kg, displayed no protective effects. The natural antioxidant beta-carotene capable of displaying antioxidative activity at low partial O2 pressures was shown to reduce the size of postinfarct scar by 34% when given in a dose of 20 mg/kg. The synthetic antioxidants, BAT and SFN-6 given in doses of 100 to 120 mg/kg each decreased antioxidant enzyme activities in the intact or infarct-related myocardium. beta-carotene was found to lack inhibitory effects on the myocardial antioxidant enzymes, thus enhancing its cardioprotective properties.