Infants born to mothers with disseminated lupus erythematosus occasionally have transient manifestations of the maternal disease. In six infants with congenital heart block born to mothers with systemic lupus erythematosus we postulated a causative relation. In one of the infants a post-mortem study of the conduction system suggested faulty embryonic development of the atrioventricular node with an abnormally thick annulus fibrosus and the effects of early inflammatory changes. Two of the infants had a cardiomyopathy and three, associated congenital heart disease.