In cases of chronic congestive heart failure, QT-interval dispersion is a strong predictor of death. Carvedilol therapy appears to decrease QT-interval dispersion. We investigated whether carvedilol reduces QT-interval dispersion in congestive heart failure and whether this pharmaceutical agent has additional effects on elderly patients. Seventy-seven ambulatory patients who had chronic congestive heart failure were evaluated for hypertension, diabetes mellitus, smoking, alcohol abuse, concomitant medications, and QT-interval dispersion. Carvedilol therapy was then initiated. Six months later, we re-evaluated the same variables, as well as morbidity and mortality rates, and number of hospitalizations. The patients were divided into 2 groups: Group I, aged < 65 years (n = 42); and Group II, aged > or = 65 years (n = 35). Statistics were analyzed with the Student's t-test chi2 test, and Cox regression model. At 6 months, both groups showed significantly decreased QT-interval dispersion values compared with baseline values (76.9 +/- 29.3 vs 104.3 +/- 41.5 ms, respectively; P < 0.0001). An elevated QT-interval dispersion value at baseline increased morbidity (P = 0.041) but not hospitalization (P > 0.05). Group II had a smaller reduction in QT-interval dispersion than did Group I (24.41 +/- 29.36 and 30.98 +/- 32.70 ms, respectively), but this difference was not significant. We conclude that in ambulatory patients with chronic congestive heart failure, long-term carvedilol therapy significantly decreases QT-interval dispersion, and this effect is uniformly distributed between patients aged < 65 years and those aged 265 years.