The effect of sulfinpyrazone (Anturane) on the extent of myocardial lesions caused by coronary ligation or isoproterenol, 5 mg/kg subcutaneously, was determined in the rat. Treatment was with sulfinpyrazone, 15 mg/kg twice daily for 5 days before the cardiac insult, or 21 days after the insult, or both. Pretreatment with sulfinpyrazone reduced isoproterenol-induced lesions by 42%. Treatment after isoproterenol had no significant effect. With coronary ligation, treatment before or after operation significantly reduced the size of infarct, pretreatment by 42%, post-treatment by 33%. The results provide evidence that sulfinpyrazone may have a clinically useful protective effect in individuals at risk of cardiac ischemia, as suggested in the Anturane Reinfarction Trial.