OBJECTIVES Effects of supplemental L-arginine, nitric oxide precursor, during warm blood cardioplegia were assessed in the blood perfused isolated rat heart. METHODS The isolated hearts were perfused with blood at 37 degrees C from a support rat. After 20 minutes of aerobic perfusion, the hearts were arrested for 60 minutes with warm blood cardioplegia given at 20-minute intervals. This was followed by 60 minutes of reperfusion. The hearts were divided into the following three groups according to the supplemental drugs added to the cardioplegic solution. The control group (n = 10) received standard warm blood cardioplegia. The L-ARG group (n = 10) received warm blood cardioplegia supplemented with L-arginine (3 mmol/l). The L-NAME group (n = 10) received warm blood cardioplegia supplemented with L-arginine (3 mmol/l) and L-nitro-arginine methyl ester, a competitive inhibitor of nitric oxide synthase (1 mmol/l). After 60 minutes of cardioplegic arrest, cardiac function, myocardial metabolism and myocardial release of circulating adhesion molecules were measured during reperfusion. RESULTS Left ventricular end-diastolic pressure was significantly lower (p<0.05) in the L-ARG group than in the control group and the L-NAME group during reperfusion. Isovolumic left ventricular developed pressure, dp/dt and coronary blood flow were significantly greater (p< 0.05) in the L-ARG group during reperfusion. The L-ARG group resulted in early recovery of lactate metabolism during reperfusion. Myocardial release of circulating intercellular adhesion molecule-1 (ICAM-1) and E-selectin were significantly less (p<0.05) in the L-ARG group at 15 minutes of reperfusion. CONCLUSIONS The results suggest that augmented nitric oxide by adding L-arginine to warm blood cardioplegia can preserve left ventricular function and ameliorate endothelial inflammation. The technique can be a novel cardioprotective strategy in patients undergoing cardiac surgery.