Correlation of left ventricular filling pressure (55 patients) with the left ventricular stroke work index (61 patients) provided a rapid means of objectively determining ventricular performance after myocardial infarction. Pressure was monitored by means of the Swan-Ganz balloon-tipped catheter and thermal indicators were used for measuring cardiac output. A hemodynamic grouping of these myocardial infarction patients on the basis of the stroke work index showed close correlation with morbidity and mortality and provided a more accurate prognostic indicator than did the commonly used clinical predictors. Serial assessment of ventricular function further aided in defining the prognosis when it was not clear on admission. Thus, the levels of normal or abnormal ventricular function and the effect of therapeutic measures can be rapidly evaluated by determining the pressures and flows in patients with acute myocardial infarction.