To the Editor.— In the article, "Hereditary Progressive Atrioventricular Conduction Defect: A New Syndrome?" by Henry T. Lynch et al (225:1465, 1973), it is stated: Five families have been reported... similar to... the family under our investigation. 1. A Lebanese family was described by Stephan in 1961 (Arch Mal Coeur5:333, 1961). Features in common with family S include... dominant inheritance, similar age at onset, and no evidence of coronary or congenital heart disease. In family S, we have evidence of a progressive atrioventricular conduction defect culminating in a complete heart block. This evidence was lacking in Stephan's family, possibly because serial ECGs over a relatively long period of time were not available to him. But in my article, serial electrocardiograms covered periods of ten and four years in two cases. Evidence of progressive atrioventricular conduction defect was quite clear in case 2 (proband). There was a 2 to 1