In order to study the effects of every part of adrenergic receptor-adenyl cyclase system on ischemic preconditioning of myocrdium in rats in vivo, SD rats were divided into three groups: IP group, I/R group and CON group. Rats were received surgical procedure and undergone left coronary artery occlusion and reperfusion. Hearts were extracted to analyze the infarct size by TTC staining, to measure serum myocardial enzymes, to study β-AR Bmax and Kd by radioligand binding assay of receptors (RAB), and to check the activity of AC and the content of cAMP by radioimmunoassay (RIA). The infarct area was found much smaller in IP group than I/R group (p<0.001); CK,CK MB and LDH were found significantly higher in I/R group (p<0.001), The Bmax of β-A R in IP group were higher than in I/R group (p<0.001), No difference of Kd could be seen between IP and I/R group, In IP group, the activity of Ac and the content of cAMP were higher than I/R group (p<0.05 and 0.001, respectively). It is concluded that ischemic preconditioning can protect the hearts from necrosis and reduce endo-enzyme leakage. The system of adrenergic receptor-adenyl cyclase system probably takes part in the protection of the IP.