This study was designed to determine if Resolvin D1 (RvD1), a pro-resolution metabolite of the omega-3 polyunsaturated fatty acid docosahexaenoic acid, could decrease myocardial infarct size with delivered at the onset of ischemia. Male Sprague Dawley rats underwent 40 minutes of myocardial ischemia followed by reperfusion. These animals received 1 intraventricular injection of RvD1 (0.01, 0.1, or 0.3 μg RvD1) or vehicle (saline) before coronary occlusion. Infarct size and neutrophil accumulation were evaluated 24 hours after the onset of reperfusion. Caspase-3, caspase-8, protein kinase B (Akt) activities were evaluated 30 minutes after the reperfusion. Rats receiving 0.1 or 0.3 μg RvD1 showed a significant decrease of infarct size and caspase-3 and caspase-8 activities compared with the vehicle controls. Neutrophil accumulations were reduced in rats administered RvD1 compared with vehicle, independently of dose level. Akt activation was increased only in animals receiving 0.1 or 0.3 μg, whereas no change was observed in the 0.01 μg group. When they were treated with LY-294002, a phosphoinositide 3-kinase (PI3K)/Akt inhibitor, cardioprotection by RvD1 was abrogated. RvD1 treatment at the onset of ischemia decreases infarct size by a mechanism involving the PI3K/Akt pathway.