OBJECTIVE: The aim of this study was to investigate the effects of exercise training on ventricular repolarization dynamicity and heart rate variability in chronic heart failure patients. DESIGN: A total of 22 chronic heart failure patients with reduced ejection fraction in sinus rhythm were included in the study. The patients were in NYHA classes II-III with an ejection fraction of 29.7 +/- 7.7%. Before and after 4 weeks of aerobic exercise training, all patients performed a cardiopulmonary exercise test, a standard twelve-lead electrocardiogram and a 24 h Holter recording from which heart rate variability and ventricular repolarization dynamicity were assessed. RESULTS: We observed a significant decrease of QTpeak (p < .001) and QTend (p < .001) at RR intervals ranging from 600 to 1000 ms on 24 h QT/RR regressions after 4 weeks of exercise training. Our analyses revealed that short-term exercise training induced significant changes in the frequency and time domain HRV parameters on an overall time-period of 24 h. CONCLUSION: Four weeks of exercise training induced significant changes in ventricular repolarization dynamicity in chronic heart failure patients. In addition, short-term exercise training was enough to improve patients\' heart rate variability.