To evaluate the ability of echocardiography to detect and localize lesions of the proximal and distal left anterior descending (LAD) coronary arteries, the systolic excursion of the left side of the septum and the ratio of septal to posterior wall excursion (IVS/PW) were measured in 26 patients with acute myocardial infarction (AMI) and nine normal control subjects. The patients with proximal LAD lesions had septal wall excursions of less than 3 mm, whereas in those with distal LAD lesions septal wall excursions were more than 3 mm. All patients with proximal LAD lesions showed an IVS/PW ratio of less than 0.4, but in those with distal LAD lesions the ratio was 0.4 or greater. We conclude that reduced or absent interventricular septal motion in anterior AMI suggests an LAD lesion, and a septal excursion of less than 3 mm suggests involvement of the proximal LAD artery, whereas septal excursion of 3 mm or more indicates involvement of the distal LAD artery.