The aim of this study was investigate the effects of carvedilol therapy on ventricular repolarization characteristics as assessed by QT dispersion (QTd) and heart rate variability (HRV) in patients with heart failure. Thirty-one patients with heart failure (mean age, 63.9 years) were included in the study. Carvedilol was administered in addition to standard therapy for CHF at a dose of 6.25 mg/day and uptitrated to the maximum tolerated dose. Control group consisted of 14 patients with heart failure (mean age, 69.4 years) who could not take carvedilol due to several reasons. All patients were followed-up 6 months. QT dispersion (QTd), and corrected QTd (QTcd) values were calculated at baseline and at the end of follow-up. Time domain and frequency domain heart rate variability analysis were performed with ambulatory Holter ECG. Mean carvedilol dose was 23.9 +/- 13.9 mg. Significant reductions were observed in the QTd (P = 0.016) and QTcd (P = 0.001) with carvedilol therapy, whereas QTd (P = 0.47) and QTcd (P = 0.43) did not change significantly in the control group. The QT maximum value did not change significantly but the QT minimum value (P = 0.03) was significantly increased after carvedilol therapy. Although the mean SDANN value was improved (P = 0.039), other HRV parameters such as mean SDNN (P = 0.32), rMSSD (P = 0.74), and the LF/HF ratio (P = 0.35) did not change significantly after carvedilol therapy. This prospective controlled study shows that carvedilol therapy decreased QT dispersion and improved ventricular repolarization characteristics but did not change autonomic dysfunction in patients with heart failure.