To investigate the effects of cellular membrane connexin 43 (Cx43) and the potential details in ischemic postconditioning (IPOC)-induced cardioprotection, ischemia/reperfusion (IR) models were generated in 8-week-old male Sprague-Dawley rats by ligating the left coronary artery anterior descending branch. The serum levels of myocardial creatases, nitric oxide (NO) and malondialdehyde (MDA) levels, infarct size, arrhythmia events, expression and distribution of Cx43, ultrastructure and apoptosis in the myocardium in different treatments with IR, IR + IPOC, IR + diazoxide or IR + IPOC + 5-hydroxydecanoate acid (5-HD) were investigated. Consequently, IPOC decreased infarct size (10.9 vs. 43.3%, P<0.01) and the levels of myocardial creatases, NO and MDA, and improved the expression (16.8 vs. 25.2% and 6.4 vs. 32.8%, after 1- and 3-h reperfusion, respectively; P<0.01) and distribution of Cx43, ultrastructure and apoptosis (19.2 vs. 42.9%, P<0.01) significantly. Diazoxide partly simulated the effects, and 5-HD attenuated but not completely abolished the effects of IPOC. In addition, the phosphorylated Cx43 (p-Cx43) level in the IR + IPOC group was lower than that in the IR + diazoxide group after 1-h reperfusion (26.1 vs. 29.4%, P>0.05); however, it was reversed after 3-h reperfusion and the p-Cx43 level in the IR + IPOC group was significantly higher than that in the IR + diazoxide group (32.8 vs. 18.7%, P<0.01). In conclusion, cell membrane Cx43 is also involved in the process of IPOC-induced cardioprotection and the improvement of membrane Cx43 is more dependent on mitochondrial KATP in the earlier phase of IPOC compared to the late phase of IPOC.