S-Nitrosylated tissue plasminogen activator (tPA) is formed by S-nitrosylation of the clinically important agent tPA by nitric oxide, thus conferring nitric oxide donor properties to the molecule. Cats were subjected to 90 min of myocardial ischemia and 270 min of reperfusion and were treated with either tPA or S-nitrosylated tPA 10 min before reperfusion. S-Nitrosylated tPA-treated cats demonstrated marked attenuation of cardiac necrosis after myocardial ischemia/reperfusion, compared with cats receiving only tPA (13 +/- 3% vs. 28 +/- 3%, P < .01). Relaxation of ischemic/reperfused left anterior descending coronary artery rings in response to the endothelium-dependent dilators acetylcholine and A23187 was greater in the S-nitrosylated tPA-treated group, compared with the cats receiving only tPA, indicating that coronary vascular endothelial function was preserved by S-nitrosylated tPA. S-Nitrosylated tPA also resulted in markedly reduced adherence of neutrophils to the coronary vascular endothelium, compared with nonnitrosylated tPA (P < .01). Immunohistochemical localization of P-selectin in the ischemic region was also significantly reduced by S-nitrosylated tPA, compared with the control group (P < .01). These data indicate that S-nitrosylated tPA is a cardioprotective agent, likely exerting its effect by site-specific nitric oxide donation resulting in inhibition of neutrophil-endothelium interaction via a P-selectin-dependent mechanism.