Objective To investigate the protection effects of different pH N 2 hydroxyethyl piperazine N′ 2 ethanesulfonic acid (HEPES) Krebs Henseleit (KH) reperfusate solutions on immature myocardium and myocardial interstitium. Methods Isolated perfused Langendorff model from immature rabbit hearts were performed. Twenty four rabbits were divided into control group, ischemia reperfusion group and acidic reperfusate group. The left ventricular function recovery, myocardial water content(MWC), lactate dehydrogenase (LDH) and creatine kinase (CK) leakage, malondialdehyde(MDA) and adenosine triphosphate (ATP) content, superoxide dismutase(SOD) activity , hydroxyproline(HP) and endothelin(ET) content were tested. Results The left ventricular functional recovery, ATP content, SOD activity and HP content in acidic reperfusate group were higher than those of ischemia reperfusion group( P lt;0.05).MWC, MDA content, CK and LDH leakage, and ET content in acidic reperfusate group were lower than those of ischemia reperfusion group( P lt;0.05). Conclusion These results suggest pH paradox might be one of important mechanisms for immature myocardium and myocardial interstitium ischemia reperfusion injury,and acidic perfusate, at the beginning of reperfusion ,might attenuate pH paradox and ameliorate functional recovery in isolated perfused immature rabbit hearts.