Objective:To investigate the protective effects of polarizing cardioplegia with Na+ channel inhibitor tetrodotoxin (TTX) on isolated rat hearts.Methods:While Langendorff and Neely perfusion model were steadily established

the rat hearts(10 hearts in each group)were respectively arrested by depolarizing cardioplegia (St.Thomas No.2 solution

STH-2)in Group Ⅰ(control group)

and by polarizing cardioplegia(TTX)in GroupⅡ.These arrested hearts were preserved in corresponding cardioplegia solution respectively at 7℃ for 5 hours and then underwent 30 minute reperfusion.Pre-ischemia and post-ischemia indexes of the rat hearts were studied

including hemodynamic parameters

myocardial enzymology

ATP content

and ultrastructural changes.Results:There were no differences between two groups before myocardial ischemia.But the recovery of myocardial hemodynamic parameters during reperfusoin in GroupⅡwas better than that in GroupⅠ(P<0.01).The leakage of CPK and LDH in GroupⅡwas less than that in GroupⅠ(P<0.05).The content of ATP in GroupⅡkept relatively higher level after reperfusion.Myocardial ultrastructures were better protected in polarizing cardioplegia group.Conclusion:Na+ channel inhibitor TTX could prevent myocardial ischemia/reperfusion injuries caused by intracellular Na+-overload and Ca 2+ -overload

and reduce the consumption of energy by arresting heart under polarizing condition.Polarizing cardioplegia(TTX) plays more effective role than depolarizing cardioplegia(STH-2) in long-term myocardial preservation of donor rat hearts.