OBJECTIVE The opening of the mitochondrial permeability transition pore (mPTP) at the time of myocardial reperfusion is a critical determinant of cell death. Emerging studies suggest that suppression of mPTP opening may underlie the cardioprotection elicited by both ischemic preconditioning (IPC) and postconditioning (IPost). To further evaluate the role of the mPTP in cardioprotection, we hypothesized that hearts deficient in cyclophilin-D (CYP-D-/-), a key component of the mPTP, will be resistant to cardioprotection conferred by ischemic and pharmacological preconditioning and postconditioning. RESULTS Male/female wild type or CYP-D-/- mice were subjected to 30 min of ischemia and 120 min of reperfusion. In wild type mice subjected to in vivo myocardial ischemia-reperfusion injury, a significant reduction in myocardial infarct size was observed with the following treatments (n>/=6/group; P<0.05): (1) IPC (28+/-4% vs. 46.2+/-4% in control); (2) Diazoxide (5 mg/kg) pre-treatment (26.4+/-3% vs. 54+/-10% in vehicle control); (3) IPost-1 or IPost-2, three or six 10-s cycles of ischemia-reperfusion (27.2+/-3% and 32+/-4%, respectively vs. 46.2+/-4% in control); (4) Bradykinin (40 mug/kg) (28.3+/-1% vs. 48+/-4% in vehicle control); (5) cyclosporin-A (10 mg/kg) (32.3+/-3% vs. 48+/-4% in vehicle control) (6) sanglifehrin-A (25 mg/kg) (29.3+/-3% vs. 48+/-4% in vehicle control). Interestingly, however, no infarct-limiting effects were demonstrated in CYP-D-/- mice with the same treatment protocols: (27.9+/-5% in control vs. 31.2+/-7% with IPC, 30.2+/-5% with IPost-1, 24.7+/-8% with IPost-2; 30.1+/-4% in vehicle control vs. 26.4+/-7% with diazoxide; 24.6+/-4% in vehicle control vs. 24.9+/-5% with bradykinin, 26.8+/-7% with cyclosporin-A, 32.5+/-6% with sanglifehrin-A: n>/=6/group: P>0.05). CONCLUSIONS This study demonstrates that the mPTP plays a critical role in the cardioprotection elicited by ischemic and pharmacological preconditioning and postconditioning.