To evaluate prospectively the prognostic value of two-dimensional echocardiography after acute myocardial infarction, two-dimensional echocardiography was performed on 61 consecutive patients who were admitted to the hospital with this condition. A left ventricular wall motion score index was derived from analysis of regional wall motion; an index of 2.0 or more within 12 hours of admission identified patients at high risk for pump failure, malignant ventricular arrhythmia or death. These complications occurred in 24 of 27 patients with an initial wall motion score index of 2.0 or more, but in only 6 of 34 with an initial index of less than 2.0 (p less than 0.0005). Of the 47 patients who were in Killip class I on admission, complications developed in 11 (79%) of the 14 with an initial index of 2.0 or more, but in only 6 (18%) of the 33 with an initial index of less than 2.0. After acute myocardial infarction, early determination of the wall motion score index by two-dimensional echocardiography is useful for identifying patients at high risk for complications and is especially valuable in the subset of patients who initially seem to be in stable condition as judged from clinical variables.