Left ventricular (LV) hypertrophy is associated with a substantial risk for malignant arrhythmias and sudden death. The effects of antihypertensive therapy on QT dispersion, which reflects cardiac repolarization heterogeneity, in relation to changes in LV mass has not been well studied. Repeat echocardiography and QT measurements (standard 12-lead electrocardiograms) were performed in hypertensive patients with LV hypertrophy, who were randomized double-blind to receive the angiotensin II type 1-receptor blocker irbesartan (n = 44) or the beta(1)-receptor blocker atenolol (n = 48) for 48 weeks, and in 37 matched hypertensive control subjects without LV hypertrophy. LV mass index was related to QT dispersion (r = 0.34, p <0.001). The reduction in LV mass was greater using irbesartan than using atenolol (-27 +/- 28 vs -15 +/- 21 g/m(2) at 48 weeks, p = 0.021), with similar reductions in blood pressure. Irbesartan decreased QT dispersion (from 56 +/- 24 ms to 45 +/- 20 ms at 48 weeks; p <0.001) and QTc dispersion (from 57 +/- 24 to 44 +/- 19 ms at 48 weeks; p <0.001). In contrast, atenolol had minor effects. The decreases in QT and QTc dispersions were greater using irbesartan than using atenolol (p = 0.001 and p = 0.011, respectively); the same results were found when changes in LV mass, blood pressure, and heart rate were also included in multivariate analyses. Thus, heterogeneity of ventricular repolarization is related to the degree of LV hypertrophy. Irbesartan, but not atenolol, reduces QT and QTc dispersions independent of changes in LV mass, blood pressure, or heart rate, and thus seems to induce structural and electrical remodeling in a direction that could decrease the risk of fatal events in hypertensive patients.