Backgroud: Transmyocardial laser revasculerization (TMLR) is considered as a new surgical technique to treat patients with intractable angina and severe coronary artery disease, especially not amenable to coronary artery bypass graft surgery (CABG) or coronary angioplasty (PTCA). Results of clinical studies continue to show that TMLR is effective in relieving angina, though its mechanism is not determined. In this experiment, we hypothesized that transmyocardial laser treament by national CO_2 laser device damages cardiac sympathetic nerve fibers that convey the pain of angina pectoris, and evaluated clinical application of TMLR to treat myocardial ischemia. Method: Left thoracotomy was performed in twenty mongrel dogs divided randomly into 4 groups(5 dogs each): Ⅰ、sham-operated negative control animals undergoing thoracotomy and pericardiotomy alone, Ⅱ、mutiple ligation of the coronary arteries to creat acute myocardial ischemia, Ⅲ、40 minutes after creation of acute myocardial ischemia, drilling with high power CO_2 laser, Ⅳ、chemical destruction of cardiac nerves by application of 85% phenol to the epicardium. 2 weeks later, the myocardium selected was prepared for examination. Cardiac sympathtic afferent nerve function and innervation was assessed by the following aspects: 1. Epicardial application of bradykinin, a potent algesic, before treatment and 2 weeks after the operation. The resulting central nervous system-mediated decrease in systemic mean arterial pressure -5- was measured. 2.The prepared myocardium was assessed by immunohistochemistry including computer image analysis, immunoblot analysis of tyrosine hydroxylase(TH), a peculiar enzyme of sympathetic nerves. 3. Regio 1 myocardial catecholamine release(norepinephrine, NE and dopamine, DA) determined by high pressure liquid chromatography (IIPLC) and electro chemical detection(EC). 4.THmRNA expression amplificated by reverse transcription polymerase chain reaction( RT-PCR). Results: Before treatment, changes in systemic arterial pressure were seen with bradykinin stimulation in all dogs. 2 weeks after treatment, no hemodynamic response was seen after stimulation of laser or phenol-treated areas, but a normal response was seen in control and ischemia groups with significant difference (P