Background: Ischemia/reperfusion (I/R) injury accelerates cardiac damage, whereas ischemic preconditioning (IPC) is cellular adaptive responses to the stress resulting in cardioprotection. Epoxyeicosatrienoic acids (EETs) by Cytochrome P450 (CYP) epoxygenases have been shown to reduce I/R injury, and PGE2 and PGI2 by Cyclooxygenase-2 (COX-2) alleviate cardiac damage in IPC. Recent studies suggested that CYP2C overexpression and 11,12-EET induce the COX-2 expression, however, the exact relation among CYPs and COX-2 in IPC has not been understood. Here, we examined the role of CYP2J3, COX-2 and its metabolites in IPC. Methods: IPC was induced by 2 cycles of each 5 min of ischemia following reperfusion before sustained 45 min I/R injury in rat hearts. CYPs or COX-2 inhibitors were added 20 min before I/R. CYP2J3 and COX-2 protein and mRNA expression were determined by Western blotting and RT-PCR. 11,12-EET was measured by LC/MS. Results: CYP2J3 expression was downregulated by I/R injury (con, 100짹3.5%; I/R, 62.5짹8.1%, p<0.01) and recovered by IPC and a nonspecific CYP inhibitor chloramphenicol (CAP). However CYP2J3 expression was not affected by COX-2 inhibitor NS-398 in IPC, CYP2J3 and COX-2 expression were inhibited by an EET antagonist, EEZE or a CYP epoxygenase inhibitor, MS-PPOH. LDH and infarct size were reduced in corresponding to CYP2J3 upregulation and production of 11,12-EET and PGE2. PPARs have been reported to regulate the expression of genes induced by I/R injury including COX-2 and CYP2J3. However, our study couldn't show the correlation of COX-2 with the activity of PPAR慣, whereas, PPAR慣 agonist enhanced CYP2J3 expression and PPAR慣 inhibitor reduced CYP2J3 and COX-2 expression. Conclusion: CYP2J3 is downregulated by I/R injury and reversed by IPC, and which is associated with enhanced PPAR慣 activity. COX-2 expression is inhibited by EEZE, MS-PPOH and COX-2 inhibitors. These data indicate that CYP2J3 expression and 11,12-EET have an important cardioprotective role in COX-2 mediated IPC.