The interlead variation in QT length on a standard electrocardiograph reflects regional repolarization differences in the heart. To investigate the association between this interlead variation (QT dispersion) and left ventricular hypertrophy, we subjected 100 untreated subjects to 12-lead electrocardiography and echocardiography. Additionally, 24 previously untreated subjects underwent a 6-month treatment study with ramipril and felodipine. In the cross-sectional part of the study, QT dispersion corrected for heart rate (QTc dispersion) was significantly correlated with left ventricular mass index (r = .30, P < .01), systolic pressure (r = .30, P < .01), the ratio of peak flow velocity of the early filling wave to peak flow velocity of the atrial wave (E/A ratio) (r = -.22, P = .02), isovolumic relaxation time (r = .31, P < .01), and age (r = .21, P < .04). In the treatment part of the study, lead-adjusted QTc dispersion decreased from 24 to 19 milliseconds after treatment, and after a subsequent 2 weeks of drug washout remained at 19 milliseconds (P < .01). The changes in left ventricular mass index at these stages were 144, 121, and 124 g/m2 (P < .01). Systolic pressure decreased from 175 to 144 mm Hg and increased again to 164 mm Hg after drug washout (P < .01). The E/A ratio (0.97, 1.02, and 1.02; P = 69) and isovolumic relaxation time (111, 112, and 112; P = .97) remained unchanged through the three assessment points. In conclusion, QT dispersion is increased in association with an increased left ventricular mass index in hypertensive individuals. Antihypertensive therapy with ramipril and felodipine reduced both parameters. If an increased QT dispersion is a predictor of sudden death in this group of individuals, then the importance of its reduction is evident.