The conduction system of seven cases died of the so-called "Pokkuri disease", was histopathologically studied with serial sectioning method. Fibrosis with a significant reduction of conduction fibers was observed in the sinoartrial node and junction between the node and atrial muscle fibers in 6 cases. Abnormal course and branching of the sinus node artery was seen in 6 cases of which 3 had no penetration of its main branch into the node. Some pathological lesions exsisted in the atrioventricular conduction system in 4 cases: 2 had fibrotic lesion in the distal bundle of His and proximal left and right bundle branches which were sandwiched between the abnormal conal muscle and the summit of ventricular septum. Remaining 2 had lipomatous partial interruption in the mid-and distal bundle of His. Simultaneous involvement of sinoartrial node and the atrioventricular conduction system was observed in 4 cases. One of such cases showed abnormal ECG consisted of a left axis deviation and right bundle branch block. As a conclusion, pathological lesions in the conduction system are revealed in more than half of cases of "Pokkuri disease/. The pathgenesis seems to be related to minor anomalies such as abnormal sinus node artery, abnormal conal muscle situation.