OBJECTIVE: Myocardial ischemia-reperfusion injury (IR) occurs frequently in the setting of hypercholesterolemia. We investigate the potential efficacy of a novel thrombin fragment (TP508) on IR injury in a hypercholesterolemic porcine model. METHODS: Twenty one hypercholesterolemic male Yucatan pigs underwent 60 min of mid-left anterior descending (LAD) coronary artery occlusion followed by 120 min of reperfusion. Pigs received either placebo (Control, n=7) or TP508 in two doses (TP508 low-dose, n=7, as bolus of 0.5 mg/kg 50 min into ischemia and an infusion of 1.25 mg/kg/hr during reperfusion period or TP508 high-dose, n=7, a double dose of TP508 low-dose group). Myocardial function was monitored throughout the experiment. The area at risk and myocardial necrosis was determined by Monastryl blue/TTC staining. Apoptosis in the ischemic territory was assessed. Coronary microvascular reactivity to endothelium-dependent and -independent factors was measured. RESULTS: Myocardial necrosis was lower in both TP508-treated groups vs. Control (p<.05). Regional left ventricular (LV) function was improved only in the TP508 high-dose group (p<.05). Endothelium-dependent coronary microvascular reactivity was greater in both TP508-treated groups (p<.05) vs. Control. The expression of proteins favoring cell survival, HSP90 and phospho-Bad (Ser112) was higher in the TP508 high-dose group (p<.05). The expression of the cell death signaling proteins, cleaved caspase-3 (p<.05), AIF (p<.05), and PARP (p=.07) was lower in the TP508 low-dose group vs. TP508 high-dose and Control. The TUNEL positive cell count was lower in both TP508 groups compared to Control (p<.05). CONCLUSIONS: This study demonstrates that in hypercholesterolemic pigs TP508 decreases myocardial necrosis and apoptosis after IR. Thus TP508 may offer a novel approach in protecting the myocardium from IR injury. Keywords: Myocardial function, Microvascular reactivity, Apoptosis, Cell survival signaling.