The left ventricular (LV) ejection fraction (EF) is known to be an independent predictor of late prognosis after acute myocardial infarction. Despite a previous report that early heart failure (evidenced only by advanced pulmonary rales in the hospital) can predict prognosis in the absence of severe depression of the LVEF at hospital discharge, the potentially strong influence of various measures of in-hospital heart failure on the predictive ability of LVEF has not been generally appreciated. Accordingly, in 972 patients with acute myocardial infarction the effect on late mortality of the presence or absence in-hospital of both clinical and radiographic signs of LV failure in subgroups of patients with normal, moderately or severely depressed LVEF was examined and measured close to hospital discharge. Patients were divided into 3 groups according to LVEF: group I LVEF less than or equal to 40, n = 265; group II LVEF 0.41 to 0.50, n = 241 and group III LVEF greater than or equal to 0.51, n = 466. When clinical signs of LV failure were present at any time during the coronary care unit period, the 1-year mortality rate after hospital discharge in groups I, II and III was 26, 19 and 8%, compared with 12% (p less than 0.01), 6% (p less than 0.01) and 3% (p less than 0.02), respectively, when signs of LV failure were absent.(ABSTRACT TRUNCATED AT 250 WORDS)