In 92 acute myocardial infarction (AMI) patients treated with tissue plasminogen activator 2.3 +/- 1.2 hours after the onset of chest pain, echocardiography was performed at 11 +/- 14 hours (early) and, in 49 patients, again at 13 +/- 7 weeks (late). Infarct location and the left ventricular wall motion score index--the average score (normal = 1, hypokinetic = 2, akinetic = 3, dyskinetic = 4) for 20 segments--were determined by 2 observers unaware of clinical, angiographic or electrocardiographic data. Concordance between noninvasive infarct location by electrocardiography or echocardiography and infarct-related artery at angiography 4 +/- 2 days later (n = 85) was 76 and 81%, respectively. The early wall motion score index was worse for anterior (1.8 +/- 0.4) versus inferior (1.3 +/- 0.2, p less than 0.0001) or posterior-lateral (1.6 +/- 0.2, p = 0.0003) infarcts. Overall, the wall motion score index improved from early to late echocardiography (n = 49, 1.5 +/- 0.3 to 1.3 +/- 0.3, p = 0.0008). However, improvement was confined to those with time to treatment less than or equal to 2 hours (n = 22, 1.4 +/- 0.3 to 1.2 +/- 0.2, p less than 0.0001), and evidence of reperfusion at angiography (n = 38, 1.5 +/- 0.3 to 1.2 +/- 0.3, p less than 0.0001). The decrease in the wall motion score index was related to a decrease in the number of adjacent involved segments (5.5 +/- 3.0 to 3.7 +/- 3.9/patient, p = 0.0006). Thus, echocardiography early after AMI identifies infarct location. Improvement in regional wall motion is seen after early treatment with intravenous tissue plasminogen activator.