Abstract: The morphology and position of atrioventricular node(AV node)and atrioventricularbundle(AV bundle) in 26 hearts (adults 5,fetuses 8,dogs 5,rabbits 8) were observed and measured underthe micr0sc0py by means of serial secti0ns. Adult AV node at the forntal section of middle part showed halfoval,flatt or fusiform in shape,the fetuses were kidney-like in shape. The size of AV n0de was 3. 7mm ×3. 5mm × 1. Omm in adult, it was 1. 1mm × 1. 8mm ×0. 6mm in fetuse,dog was 2. 1mm × 2. 4mm × 0.6mm, rabbit was 2. 1mm × 1. 2mm × 0. 4mm. The size of AV bundle in adult was 7. 4mm × 2. 2mm × 1.2mm. The adult AV node was 3. 0-4. 0mm posterior to the anterior border o cronory sinus orifice,0. 2-0. 6mm from the endocardium of right atrium, 1. 9-5. 5mm above the upper border of the septal leafletof the tricusipid valve. Their clinical significance was discussed.