Résumé : Body surface potential maps were recorded from 120 electrode sites in 236 normal subjects and 258 patients with initial evidence of either anterior myocardial infarction (MI) or inferior MI to identify characteristic map patterns in both groups. After time normalization, averaged map distributions were displayed at 18 equal time intervals during both QRS and ST-T waveforms from the normal, anterior MI and inferior MI groups. At each time instant, the 120-point averaged normal map was subtracted in turn from the corresponding anterior and inferior MI maps; the resulting differences at each electrode site were divided by the pooled standard deviation and the obtained values (discriminant indexes), plotted as contour lines with 1 standard deviation increments, producing discriminant maps for each bigroup comparison. The most consistent discriminant patterns in 114 patients with anterior MI were observed in early QRS in the upper left anterior chest where abnormal negative voltages reflected loss of electric potentials while reciprocal changes were noticed in the lower back; by mid-QRS, both distributions had moved jointly and vertically, the former in the lower torso on the midsternal line, the latter in the upper back. In 144 patients with inferior Ml, abnormal positive distributions were observed in early QRS in the upper back, followed later by excessive negative voltages in the inferior right anterior chest; at mid-QRS, both distributions had migrated horizontally, the former proceeding toward the upper anterior torso, the latter to the lower left dorsal area. Abnormal negative voltages were seen in the precordial region during ST in the inferior MI group, moving toward the lower left flank where they stayed throughout T; in the anterior MI group abnormal negativities appeared in the precordial area at the beginning of T and remained there until the end of repolarization. Intragroup variability was investigated by producing scattergrams of extrema and of abnormal peak discriminant indexes (≥2 standard deviations) derived from individual patients within each population. The presence of electrocardiographic subgroups was suggested for both classes of infarction: anterior MI with or without apical involvement in the anterior group and inferior-posterior MI with or without right ventricular involvement and with or without apical extension in the inferior group. Thus, both types of infarction share a temporally common but spatially discriminating portion of the early QRS. Repolarization patterns in both infarction groups were also spatially discriminant from normal subjects, but temporally heterogeneous one from the other. Retrospective classification of patients based on the presence of one or more patterns typical in time and in location of their respective groups yielded 96% and 93% of correct assignment to the anterior MI and the inferior MI classes, respectively. The specificity was 94% for normal control subjects. © 1987.