Objective To observe the change of sino-atrial nodal tissue structure and ectopic pacing function after xenogenic sino-atrial nodal tissue transplanted into left ventricular wall, so as to provide new ideas for the treatment of sick sinus syndrome and severe atrioventricular block. Methods Seventy healthy rabbits were selected, male or female, and weighing 1.5-2.0 kg. Of them, 42 were used as reci pient animals and randomly divided into sham operation group, warm ischemia transplantation group, and cold ischemia transplantation group (n=14), the other 28 were used as donors of warm ischemia and cold ischemia transplantation groups, which were sibl ing of the recipients. In recipients, a 6-mm-long and about 2-mm-deep incision was made in the vascular sparse area of left ventricular free wall near the apex. In sham operation group, the incision was sutrued directly by 7-0 Prolene suture; in cold ischemia transplantation group, after the aortic roots cross-clamping, 4 ℃ cold crystalloid perfusion fluid infusion to cardiac arrest, then sinoatrial node were cut 5 mm × 3 mm for transplantation; in warm ischemia transplantation group, the same size of the sinus node tissue was captured for transplantation. After 1, 2, 3, and 4 weeks, 3 rabbits of each group were harvested to make bradycardia by stimulating bilateral vagus nerve and the cardiac electrical activity was observed; the transplanted sinus node histology and ultrastructural changes were observed. Results Thirty-six recipient rabbits survived (12 rabbits each group). At 1, 2, 3, and 4 weeks after bilateral vagus nerve stimulation, the cardiac electrical activity in each group was significantly slower, and showed sinus bradycardia. Four weeks after operation the heart rates of sham operation group, warm ischemia, and cold ischemia transplantation group were (81.17 ± 5.67), (82.42 ± 7.97), and (80.83 ± 6.95) beats/ minute, respectively; showing no significant difference among groups (P gt; 0.05). And no ectopic rhythm of ventricular pacing occurred. Sino-atrial nodal tissue survived in 6 of warm ischemic transplantation group and in 8 of cold ischemia transplantation group; showing no significant difference between two groups (P gt; 0.05). Two adjacent sinoatrial node cells, vacuole-l ike structure in the cytoplasm, a few scattered muscle microfilaments, and gap junctions between adjacent cells were found in transplanted sinus node. Conclusion The allograft sinus node can survive, but can not play a role in ectopic pacing.