The QT interval is a clinically important electrocardiographic measurement. This study attempted to determine 1) whether this interval was spatially distributed in a physiologically meaningful way on the torso of normal subjects, and 2) if these spatial patterns were altered in patients with acute myocardial infarction. To do so, 30 patients were studied within 72 hours of the onset of acute myocardial infarction (15 with an anterior and 15 with a posterior lesion) along with 50 normal control subjects. Electrocardiographic signals were registered from 150 torso electrodes; the QT interval in each lead was determined by a combined automated-manual method, and the durations displayed as "isointerval maps." In the normal subjects, the difference between the longest and shortest interval in each case was 59.4 +/- 12.9 ms. Long QT intervals were spatially located over the left lateral torso and short QT intervals were found over the right inferior chest. Acute infarction modified this distribution in relation to lesion location; the longest QT intervals were centrally positioned in anterior infarction and caudally located in inferior infarction. Thus, QT intervals in normal and abnormal states have distinctive spatial distributions that are consistent with known regional myocardial electrophysiology.