A group of 300 institutionalized individuals, average age, 82 years, was followed from the onset or discovery of an intraventricular conduction disturbance to death over an average period of more than five years. They included 143 cases with left anterior hemiblock, 60caseswith left bundle branch block, and 97 cases with right bundle branch block with and without left anterior or posterior hemiblock. Twenty-two cases developed second or third degree heart block. The magnitude of risk of developing second or third degree heart block averaged 1.5% per year for the first five years of follow-up and 2.5% per year for the next four years of follow-up. For the first five-year period of follow-up the magnitude of risk was 6.976, and for the entire nine-year period of follow-up 15.7%. An intraventricular conduction disturbance was found before death in 20% of tetranitrate is a physiologically effective long-acting agent in patients with coronary heart disease.