Abstract: To explore the myocardioprotective effect and mechanism of adenosine preconditioning in patients undergoing open heart surgery. Methods：Twentythree patients with simple congenital heart defects were randomly divided into two groups：adenosine preconditioning group (adenosine group，n=12) and control group (n=11). The hearts suspended with cool improved St.Thomas cardioplegia (20?ml·kg-1) which was perfused every thirty minutes after aorticclamping in both groups. Adenosine was administered intravenously to the patients slowly in adenosine group at a dose of 2?mg·kg-1 before beginning of cardiopulmonary bypass(CPB). The serum concentration of creatine kinase(CK), creatine kinase MB isoenzyme (CKMB) and lactic dehydrogenase(LDH) from venous blood were measure at different time points after operation. Myocardial tissues were taken from right atrial appendage at the end of the myocardial ischemia time，and the cytohistomorphological changes were observed. Results: After heartreperfusion，the proportion of spontaneous returned heartbeat was 91.6% in adenosine group，but 54.5% in control group (P<0.05). The levels of serum CK, CKMB and LDH in adenosine group were much less than those in control group at different time points(P<0.05 or P<0.01).　The myocardial histomorphological observation showed very metamorphic changes in control group, but slighter changes in adenosine group. Conclusion: Adenosine preconditioning can reduce the release of myocardial enzyme and the ischemic injury of myocardium, which may be one of the mechanisms of adenosine preconditioning.reperfusion，the proportion of spontaneous returned heartbeat was 91.6% in adenosine group，but 54.5% in control group (P<0.05). The levels of serum CK, CKMB and LDH in adenosine group were much less than those in control group at different time points(P<0.05 or P<0.01).　The myocardial histomorphological observation showed very metamorphic changes in control group, but slighter changes in adenosine group. Conclusion: Adenosine preconditioning can reduce the release of myocardial enzyme and the ischemic injury of myocardium, which may be one of the mechanisms of adenosine preconditioning.

Key words: Preconditioning, adenosine, Myocardial ischemia, Cardiac surgical procedures