One hundred eighty of 1260 patients consecutively admitted to the hospital because of unstable angina pectoris had the typical ST-T segment changes suggestive of a critical stenosis in the proximal LAD. In 108 patients the ECG abnormalities were present at the time of admission. In the remaining 72 patients they developed shortly there-after. The difference between these two groups was a longer duration of anginal complaints in the former (mean 2.3 days). Results of coronary angiography, performed a mean of 4.6 days after the last attack of chest pain, showed 50% or more narrowing in the proximal LAD in all patients. Thirty-three patients had complete occlusion of the LAD and 75 had collateral circulation to the LAD. Results of left ventricular angiography showed abnormal systolic left ventricular wall motion in 137 patients and normal systolic motion in the remaining 43 patients. The difference between these two groups was a shorter mean time interval between the last attack of chest pain and angiography in the former group ( p < 0.001). Twenty-four patients had only abnormal diastolic wall motion. Twenty-one patients had a small increase in the creatine kinase level at the time of admission. Fifteen patients (nine before and six during early revascularization) had an anterior wall myocardial infarction in the hospital; these patients had a patent but severely narrowed LAD and a low incidence of collateral circulation to the LAD. One hundred fifteen patients underwent revascularization shortly after admission. Of 56 patients treated medically, 26 eventually underwent revascularization (a mean of 8 months and 15 days after the initial admission). During the follow-up period (mean 4.2 years) eight of the 30 patients treated medically died of a cardiac cause. There was one cardiac death among the 136 patients discharged after revascularization. During follow-up most of the patients showed normalization of the ECG and left ventricular wall motion abnormalities, suggesting hibernation or stunning of the myocardium as the mechanism of these abnormalities. We conclude that in risk stratification of patients with unstable angina, the ECG is of great value for recognizing a subset of patients with a proximal LAD lesion having a poor prognosis because of a substantial area of jeopardized myocardium. Early cardiac catheterization is indicated so that appropriate therapy can be selected.