Significance of U wave polarity in patients with a prior inferior myocardial infarction. Sixty consecutive patients who underwent coronary angiography and left ventriculography from six to eight weeks after the onset of definite inferior myocardial infarction were divided into three groups according to the polarity of U waves in (1) leads II, III, a VF and (2) in leads V4 to V6 (positive = Group P, flat or isoelectric = Group F, and negative = Group N). The following parameters were analyzed: (1) ECG score; (2) global ejection fraction: (3) regional area change: (4) number of asynergic, and akinetic segmental radii; (5) number of asynergic and akinetic areas: and (6) number of diseased coronary arteries and the incidence of left anterior descending artery (LAD) disease. There were no significant differences among the three groups according to the polarity of U waves in two subgroups by the site of U waves in age, gender, systemic blood pressure, and ECG scores. The polarity of U waves in leads II.III.a VF (subgroup 1) correlated with the size of myocardial infarction; regional area changes in inferior segment (Area 2) were 64.1 +/- 8.2 in group P1, 31.8 +/- 14.7 in group F1, and 21.0 +/- 15.8 in group N1 (p less than 0.01, F = 32.8). The polarity of U waves in leads V4-6 (subgroup2) correlated with anterolateral wall motion; regional area changes in anterolateral segments (Area 5) were 76.8 +/- 11.6 in group P, 66.5 +/- 18.5 in group F, and 48.9 +/- 17.1 in group N (p less than 0.01, F = 18.6). The incidence of multivessel disease increased from group P2 (36.4%), to group F2 (54.5%), to group N2 (75.0%), and the incidence of LAD disease increased from 27.3%, to 45.5%, to 68.8%, respectively. A negative U wave in either location suggested severely decreased apical wall motion, and there was a tendency for global ejection fractions to decrease in the following order: group P, group F, and group N. From these results, the authors conclude that the polarity of U waves may be one of the parameters correlating with the wall motion and left ventricular function in prior inferior myocardial infarction. 