<正> A new experimental extracorporeal circulation （ECC） in vivaheart was established in three randomized groups of eight rabbits each.Group I received insulin （6U/kg） together with a 50% glucose infusion（6g/kg） and potassium （1.2mEq/kg）（GIK） before operation

while group Ⅱreceived Ringer’s lactate solution and group Ⅲ received 50% glucosesolution at the same infusion rate. Forty minutes after ischemia

biopsiesof the heart were made in order to analyze the tissue contents of adenosinetriphosphate and creatine phosphate by means of bioluminescent technique.Myocardial glycogen level was examined by electron microscopy. The meanadenosine triphosphate content in group I was 6.31μ mol/g and wassignificantly （P<0.01） higher than that of group Ⅱ （3.63μ mol/g） andgroup Ⅲ（2.99 μ mol/g）. The mean creatine phosphate content of group I

（4.02μ mol/g）

was also significantly higher than that of group Ⅱ （2.13μmol/g）（P<0.05）. The content of creatine phosphate of group Ⅲ was 3.20 μmol/g

with approximately significant difference as compared with group I.The myocardial ultrastructure of group I showed higher level of myocardialglycogen after ischemia. It is concluded that the preoperative use of GIKmay augment the storage of myocardial adenosine triphosphate

creatinephosphate and glycogen

which might enhance the myocardial tolerance toischemia.