The influence of trimetazidine on infarct size was studied with a 45-minute period of coronary occlusion followed by 24 hours of blood reperfusion in the rabbit heart. The groups studied were 7 control rabbits and 7 rabbits pretreated with 3 mg/kg of trimetazidine. Twenty-four hours after coronary artery ligation for 45 minutes, infarct size was measured in myocardial slices using trinitrophenyl tetrazolium staining, and the area at risk was determined by injection of zinc/cadmium particles and delineated at the same time by imaging, under fluorescent light, the areas of tissue that fluoresced. The range of area at risk was similar in both of the groups. There was a significant reduction in the size of infarct that developed in the trimetazidine-treated group when compared with the control rabbits. It is concluded that pretreatment with trimetazidine in the blood-perfused rabbit heart is effective in reducing myocardial infarct size.