Ischemic postconditioning (IPCD) significantly reduces infarct size in healthy animals and protects the human heart. Because obesity is a major risk factor of cardiovascular diseases, the effects of IPCD were investigated in 8-10 weeks old leptin-deficient obese mice (ob/ob) and compared to wild-type C57BL/6J mice (WT). All animals underwent 30 min of coronary artery occlusion followed by 24 h of reperfusion associated or not with IPCD (6 cycles of 10 s occlusion/10 s reperfusion). Additional mice were sacrificed at 10 min of reperfusion for Western blotting. In WT mice, IPCD reduced infarct size by 58% (33±1% vs 14±3% for control and IDPC, respectively, p<0.05) but failed to induce cardioprotection in ob/ob mice (53±4% vs 56±5% for control and IPCD, respectively). In WT mice, IPCD significantly increased the phosphorylation of Akt (+77%), ERK 1/2 (+41%) and their common target p70S6K1 (+153% at Thr 389 and +57% at Thr 421/Ser 424). In addition, the phosphorylated AMPK to total AMPK ratio was also increased by IPCD in WT mice (+64%, p<0.05). This was accompanied by decreases in PTEN, MKP-3 and PP2C levels. In contrast, IPCD failed to increase the phosphorylation state of all these kinases in ob/ob mice and the level of the 3 phosphatases were significantly increased. Thus, although IPCD reduces myocardial infarct size in healthy animals, its cardioprotective effect vanishes with obesity. The lack of enhanced phosphorylation by IPCD of Akt, ERK 1/2, p70S6K1 and AMPK might partly explain the loss of cardioprotection in this experimental model of obese mice.