The implantable cardioverter-defibrillator (ICD) increases survival of patients who receive the device. However, candidacy rates have not been calculated for a defined population, and the potential effect of the device on the survival of all patients with heart disease has not been estimated. To make these calculations, medical records were reviewed for 1976 to 1988 in a population demographically similar to the white population of the United States. Definite and possible candidates were identified on the basis of American Heart Association /American College of Cardiology guidelines. Candidacy rates ranged from 3.3 100,000 (counting only definite candidates for the entire period) to 8.7 100,000 (counting definite and possible candidates after 1980). Extrapolated to the 1990 U.S. population, estimates ranged from 8,207 to 21,637 new candidates each year. During an average follow-up of 5 years, half of all deaths among candidates had the potential to be delayed by an ICD. In a similar population that has a death rate from heart disease of approximately 280 100,000, 0.6 to 1.6% of subjects have the potential to have their deaths delayed to some extent by an ICD.