Marked bradycardia in persons in middle or later life was first described by Morgagni in 1761. It is only in recent years, however, that accounts of the condition in children have appeared. In nineteen instances, the bradycardia apparently was due to congenital heart block. This disorder in infants is sufficiently rare to warrant the recording of an additional case.It is evident that the diagnosis of congenital heart block can rarely be proved because of the lack of exact observations on fetal heart rates. This condition, however, must be seriously considered in a child with a slow pulse rate when a history of acquired disease, such as diphtheria, rheumatic fever, syphilis or severe pyogenic infection is not obtained. The accepted cases were proved by electrocardiograms or pulse tracings. Graphic proof of heart block was delayed until later years in several instances, but in these a history of some circulatory disorder,