To Identify the patient at high risk after acute myocardial Infarction data on 400 patients obtained from the Myocardial Infarction Research Units Cooperative Data Bank were examined. Patients were grouped according to clinical findings as follows: uncomplicated (class 1, 81 patients); mild to moderate failure (class II, 150 patients); severe failure with pulmonary edema (class III, 17 patients); and severe failure with shock (class IV, 152 patients). Hemodynamic data Including pulmonary capillary wedge pressure and cardiac output were available In all patients. High risk subsets within clinical classes I, II and IV were Identifiable. In class I, nonsurvivors had significantly (P <0.05) higher values for pulmonary capillary wedge pressure (16 mm Hg) and heart rate (96 beats/min); nonsurvivors In class II also had a significant (P <0.01) elevation In pulmonary capillary wedge pressure (23 mm Hg); and In class IV the high risk subset was characterized (P <0.01) by pulmonary capillary wedge pressure (21 mm Hg), heart rate (100 beats/min), cardiac Index (1.6 liters/min per m2), stroke index (14 cc/m2) and stroke work index (12 g-m/m2). Discrimlnant function analysis using pulmonary capillary wedge pressure and heart rate predicted mortality In classes I to III with 72 percent accuracy; a similar equation representing stroke work index, pulmonary capillary wedge pressure and cardiac Index had an 83 percent rate of accuracy in class IV patients. interclass comparison of the last three measurements indicated that the data differed significantly among classes, thus signifying a spectrum of ventricular impairment after Infarction that was commensurate with the clinical presentation. However, in individual patients the clinical examination did not consistently reflect the degree of ventricular dysfunction. Thus, careful bedside examination together with hemodynamic monitoring of wedge pressure, cardiac output and heart rate serve to identify the high risk patient after acute myocardial infarction.