Patients with non-Q-wave myocardial infarction and unstable angina fall between these two extremes. In the days and weeks following the onset of their disorder, their prognosis for survival is better than that of patients with Q-wave myocardial infarction but worse than that of patients with stable angina. Some patients with unstable angina progress to acute myocardial infarction, and some of those with non-Q-wave infarction experience an unstable course with reinfarction. Although others recover from the acute episode without subsequent infarction or reinfarction, they frequently have severe obstructive coronary artery disease and may be left with severe chronic stable angina. National summaries of hospital records indicate that 750,000 patients are hospitalized yearly with unstable angina and 250,000 with non-Q-wave myocardial infarction.