We studied 16 patients, 36 to 75 years old, with repetitive episodes of spontaneous angina (SA) associated with transient ST-segment shifts. At onset SA was not associated with changes in systolic blood pressure, heart rate, or double product, but such increases often occurred late. All patients smoked cigarettes; 13 were hypertensive. History of angina at rest or exertion was present in 13 patients, seven of whom had crescendo chest pain before admission. Twelve patients had an acute myocardial infarction (MI). Complications were not uncommon in the setting of MI. Angina persisted in a few patients after MI, and resulted in its extension in three patients. Coronary arteriography performed on eight patients revealed significant coronary artery disease in seven. There was a good correlation between the loci of coronary lesions and the transient ECG changes. Nitrates were occasionally ineffective in relieving symptoms and failed to prevent SA. High doses of propranolol were also ineffective. Aortocoronary bypass surgery was performed on three patients. Fifteen patients were discharged asymptomatic. One patient died in the hospital. Three additional patients died within the first month after admission. Followup in the clinic revealed good response to nitrates in the 12 surviving patients. SA in the CCU may be a good model to study the pathogenesis of myocardial ischemia and acute MI.