Two case reports of patients known to have complete heart block for 35 years are presented for the purpose of adding to the literature further information on the important aspect of prognosis in this disease of the heart. Atrioventricular block has always been an important clinical problem in itself and also in indicating the existence of serious disease or toxic states. Occasionally, however, and possibly more often than is generally appreciated, etiological factors may influence strikingly the course of this disease. REPORT OF CASES Case 1.— Miss L. W., aged 57, a white registered nurse, was known to one of us (J. E. B.) for 35 years. In 1910, when she was hospitalized for a minor surgical procedure, it was noted that she had a "slow pulse." The patient's mother told her that when she was very young the family doctor had observed her unusually slow pulse rate. She had