Background Cardiac resynchronization therapy (CRT) is a well established treatment in selected patients with heart failure. The non physiological ventricular activation sequence has been implicated in the occurrence of sudden death after CRT. There is conflicting date concerning the effect of different pacing modes on ventricular repolarization in heart failure patients. Purpose Assessing the effects of biventicular (Bi V), left ventricular (LV) epicardial pacing and right ventricular endocardial pacing (RV) on QT intervals (QT end, QT apex, JT) and transmural dispersion of repolarization (TDR) in patients with heart failure having CRT. Methods 20 patients (15 men and 5 women, age = 63.4 ± 11 years) with NYHA III-IV heart failure due to left ventricular systolic dysfunction and cardiac dyssynchrony received CRT. We measured QT end intervals, JT intervals and TDR according to recommended methods on a 12 lead ECG recorded at baseline and after implant. After implant, ECG was recorded with temporary right ventricular pacing, temporary left ventricular pacing and then the final pacing mode : simultaneous biventricular pacing. Results There was no significant difference between QT end interval, JT interval and TDR at baseline and after implant with different pacing modes. Conclusion In our study, we noticed no effect of pacing modes on repolarization in patients with heart failure. The high incidence of sudden death observed in CRT may be explained by competitvity of modes of death rather than induced abnormal repolarization.