Heart conductive system (HCS) including the sinoatrial node (SAN), atrioventricular node (AVN), AV bundle (AVB) and its left and right parts was studied histologically. It is shown that different portions of HCS are damaged in diphtheria with different frequency and intensity, the frequency depending on the depth of their location. Left part of AVB is affected most frequently, followed by the right part of AVB, AVB, AVN and the least frequently SAN.