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The constant evolution of medical knowledge and accompanying developmentof diagnostic and treatment possibilities for arrhythmias and conduction distur-bances has reawakened interest in the structure and function of the conductionsystem of the human heart, especially in the region of the atrioventricular (AV)junction and within the junction itself. Of the large number of studies dealingwith the AV junction few focus on the initial zones of the AV node. These weredescribed for the first time by Tawara in 1906. Similarly, Anderson et al. distin-guished two origins of the AV node, the left one running towards the basis ofthe mitral valve and the right one leading towards the tricuspid valve. The differ-ences in length and scale could be the result of the adoption of different refer-ence points.The study was carried out on the material of 50 human hearts, of both sexesand ranging in age from 22 to 93, which were fixed in 10% formalin and 98%ethanol solution. The tissue obtained was fixed in the 10% formalin solutionand, after being sunk in the paraffin, was cut into layers of about 10 µm thick.According to the age of the hearts, every 10