A cohort of 76 patients with acute myocardial infarction was studied with infarct-avid scan, radionuclide ventriculography, and thallium-201 myocardial perfusion scintigraphy. Infarct area, left ventricular ejection fraction, and defect score were calculated as radionuclide indices of the extent of myocardial infarction. The correlation was studied between these indices and cardiac events (death, congestive heart failure, postinfarction angina, and recurrence of myocardial infarction) in the first postinfarction year. High-risk patients (nonsurvivors and patients who developed heart failure) had a larger infarct area, a lower left ventricular ejection fraction, and a larger defect score than the others. Univariate linear discriminant analysis was done to determine the optimal threshold of these parameters for distinguishing high-risk patients from others. Radionuclide parameters obtained in the early phase of acute myocardial infarction were useful for detecting both patients with grave complications and those with poor late prognosis during a mean follow-up period of 2.6 years.