Various pharmacologic interventions that suppressed chemotactic factor activity in the coronary sinus after acute ischemia were analyzed for protective effects on myocardium. Ischemic injury was determined by comparing the slopes of the regression lines derived from 24 hour myocardial creatine kinase content versus S-T segment elevation 15 minutes after coronary ligation. Dogs treated 30 minutes after ligation with cobra venom factor, hydrocortisone or Trasylol showed a marked decrease in chemotactic activity in the coronary sinus. These agents also showed a protective effect on ischemic injury when compared to control. Myocardial biopsy specimens from areas of significant ischemia defined by S-T segment elevations in dogs treated with cobra venom factor were essentially devoid of an inflammatory response whereas those from dogs treated with Trasylol or hydrocortisone showed moderate neutrophil infiltration and minimal tissue exudate.