AIM: To investigate the role of catecholamine, angiotensin converting enzyme(ACE) and adenosine triphosphatase in ischemic preconditioning in isolated rat hearts. METHODS: Isolated perfused rat heart was subjected to global ischemia for 40 min followed by reperfusion for 10 min (I/R). Preconditioning (PC) was induced by 5 min of ischemia and 10 min of reperfusion. The tissue concentrations in NE, and ACE, ATPase activities were determined in left ventricle in the PC and I/R groups by fluorometry and spectrophotometry. RESULTS: There were no significant difference in NE and ACE between PC and I/R groups. PC hearts showed improved recovery of the contractile function after 40 min ischemia/10 min reperfusion, but activities of the myocardial total ATPase, Mg2＋-ATPase, Na＋K＋-ATPase were inhibited markedly compared with I/R group. CONCLUSION: The inhibited myocardial ATPase may be involved in the mechanism of ischemic preconditioning protection in the isolated rat heart. Endogenous myocardial norepinephrine and ACE activation are not essential for ischemic preconditioning in the isolated rat heart.