Phosphodiesterase-5 (PDE-5) inhibitors including sildenafil and vardenafil induce powerful preconditioning-like cardioprotective effect against ischemia/reperfusion injury through opening of mitochondrial K ATP channels in the heart. The goal of these studies was to demonstrate the protective effect of sildenafil and vardenafil on reperfusion injury and to compare it with the antianginal vasodilator nitroglycerin (NTG). In addition, we determined the role of mitochondrial K ATP channels in protection. Adult male New Zealand white rabbits were anesthetized and subjected to ischemia by 30 min of coronary artery occlusion followed by 3 hrs of reperfusion. Seven groups were studied. 1-Controls; 2-Sildenafil (total dose: 0.71 mg/kg; iv) infused for 65 min starting 5 min before reperfusion; 3-Sildenafil+5-hydroxydecanoate (5-HD, blocker of mitochondrial K ATP channel, total dose: 5 mg/kg) administered as 2 bolus injections; 4-Vardenafil (total dose: 0.014 mg/kg; iv) administered as in group 2; 5-Vardenafil+5-HD administered as in group 3; 6-5-HD administered as two bolus injections and 7-Nitroglycerin (NTG, total dose: 2 μg.kg -1.min -1) administered as in group 2. Infarct size was reduced in sildenafil (19.19±1.3%) as well as vardenafil (17.0±2.0%) treated groups as compared to controls (33.8 ± 1.7%). However, NTG failed to confer similar cardioprotection (31.5±0.8%). 5-HD blocked the cardioprotective effects of sildenafil and vardenafil as shown by an increase in infarct size (34.0 ±1.1% and 28.3±1.9%, respectively). Both sildenafil and vardenafil protect the ischemic myocardium against reperfusion injury through a mechanism dependent on mitochondrial K ATP channel opening. Future clinical trials are needed to exploit the potential utility of PDE-5 inhibitors in cardioprotection in patients with coronary artery disease.