Abstract: Ohjective: To study the morphological aspects corresponding to the complex electrophysiological signs of dual (multi) -pathway and reentry of the atrioventricular node (AVN) area. Methods: The architecture of the specialized myocardial fibers of the AVN area was observed under microscope with serial section in 18 rats. Results: ①The rat AVN lay in the right side of center fiber body. The posterior part appeared thin and broad, the middle thick and the anterior narrow. ②The AVN can be divided into a superficial layer and a deep layer. The superficial layer containing vertical specialized fibers circled the deep layer. The deep layer which fibers arranged from the posterior to the anterior can be subdivided into an upper part and a lower part. In the anterior part of the AVN, the lower part became gradually large and was into the AV bundle. ③The AVN composed of four types cells, P cell, T cell, Purkinje cell and normal cardiac working cell. ④The overlaying on the AVN is a transition area between atrial muscle and the AVN . There were many connecting fibers between the overlaying and the AVN. A few fibers in the overlaying connected with ventricular muscle. ⑤The AVN linked the atrial muscle in several routes. In four specimens, there were some connecting fibers between the AVN and ventricular muscle. Conclusion: In the AVN area, the superficial and deep layers, the upper and lower parts and the connections between the AVN and atrium or ventricular may be the morphological bases of dual or multi pathways conducting and reentry.