The protective effects of trimetazidine on postischemic cardiac function were studied using isolated working rat heart preparations in which global ischemia had been induced with normothermic cardioplegia. After 30 minutes of reperfusion, following a 25 minutes period of ischemia, the addition of 10(-6) M or 10(-5) M trimetazidine to the cardioplegic solution significantly increased the per cent recovery of the cardiac output: from 54.8 +/- 4.1 per cent in the control group to 81.0 +/- 3.2 per cent (p less than 0.01) and 79.6 +/- 4.0 per cent (p less than 0.01), respectively, although lower (10(-7) M) or higher (10(-4) M) doses of the drug failed to result in any change. 10(-5) M trimetazidine also produced a significantly greater recovery of both the postischemic aortic flow: from 47.8 +/- 4.9 per cent to 72.2 +/- 3.8 per cent (p less than 0.01) and coronary flow: from 80.6 +/- 2.9 per cent to 105.2 +/- 6.3 per cent (p less than 0.002). However, trimetazidine did not influence the recovery of either aortic pressure or heart rate. These results suggest that trimetazidine does give some protection to the heart during ischemia and reperfusion.