A daily nitrate-free interval (NFI) lasting 4-7 hours was instituted in four patients with severe congestive heart failure secondary to myocardial ischemia who were awaiting orthotopic heart transplantation. The duration of intravenous nitroglycerin therapy ranged from 14-55 days, and the maximum dosage was 50-400 microg/minute. Anginal events occurred more frequently during the NFI than during intravenous therapy. An NFI of 8-12 hours reduces tolerance in patients with congestive heart failure and stable angina. However, the experience in these patients with recurrent ischemia does not support its use to prevent ischemic events during hospitalization.