To recognize patients prone to subsequent left ventricular dilation after the acute phase of a myocardial infarction treated with thrombolysis, we studied 233 patients with a first anterior infarction, treated with thrombolysis, with 2-dimensional echocardiography within 12 hours after admission and 3 months later. A wall motion score index (WMSI) and left ventricular volumes were assessed, and enzymatic infarct size was expressed as cumulative alphahydroxybutyrate dehydrogenase determined in the first 72 hours after infarction. Patients who died (17 of 233, 7%) after a mean follow-up of 517 days had a significantly higher acute WMSI (2.1 +/- 0.3, mean +/- SD) than those who survived (1.9 +/- 0.4)(p=0.006). With use of this cutoff value for 2 WMSI, ventricles with an acute WMSI < or = 2 (62%) showed no increase in end-diastolic volume index (EDVI) or end-systolic volume index (ESVI), whereas ventricles with an acute WMSI >2 (38%) showed a significant increase in ESVI (6.1 +/- 12.2 ml/m2) and in EDVI (10.3 +/- 16.6 ml/m2) in the first 3 months. Using a cutoff value of 1,000 U/L for cumulative alphahydroxybutytrate dehydrogenase, only infarcts with a value of >1,000 U/L (52%) caused a significant increase in EDVI (10.8 +/- 14.3 ml/m2) and ESVI (6.5 +/- 10.0 ml/m2) in the first 3 months. Thus, acutely assessed WMSI of >2 can readily predict subsequent dilation in patients with a first anterior infarction treated with streptokinase and is a good predictor of mortality. Enzymatic infarct size also is a predictor of dilation, although not available until 3 days after infarction.