A case report of a 19-year-old male with atherosclerosis and diffuse myocardial fibrosis is given. Serial sections showed that the right bundle branch was absent. This defect was due to failure of the right bundle branch to develop. A single electrocardiogram was taken, interpreted as an indeterminate form of intraventricular block with lesions probably of both ventricles. The author discusses the embryology of the development of the conduction system.