Recent studies have demonstrated that cyclooxygenase-2 (COX-2) is an essential mediator of the cardioprotective effects of the late phase of ischemic preconditioning (PC) in rabbits. The goal of this study was to determine whether COX-2 also plays an essential role in late PC in the mouse. B6129F2/J mice underwent a 30-min coronary occlusion followed by 24 h of reperfusion. Administration of the COX-2 selective inhibitor, NS-398, 30 min prior to the 30-min occlusion (5 mg/kg i.p.) had no appreciable effect on infarct size compared with untreated controls (58.8 +/- 2.1%, vs. 58.8 +/- 4.3% of the risk region, respectively). When mice were preconditioned with six cycles of 4-min coronary occlusion/4-min reperfusion 24 h prior to the 30-min occlusion, infarct size was markedly reduced (19.3 +/- 3.4%), indicating a late PC effect. The protective effect of late PC was completely abrogated by administration of NS-398 30 min before the 30-min coronary occlusion (67.7 +/- 3.0%), but not by administration of vehicle alone (23.6 +/- 3.7%). These results indicate that COX-2 mediates the late phase of ischemic PC in the mouse and imply that the role of this enzyme in cardioprotection is not species-specific.