Background Reverse electrical remodeling (RER) is usually assessed by measuring the QRS duration (QRSd) before and after cardiac resynchronization therapy (CRT) during the stimulator off. The ventricular electrical depolarization dyssynchrony (DYS) can be assessed directly from ECG by high frequency QRS analysis. The purpose of the study was to compare the RER assessment by the DYS and QRSd changes in CRT patients. Method In 26 consecutive CRT recipients (all left bundle branch block), echocardiography and 14-lead ECG (sampling 5kHz/24bits, 5 min measurement) were conducted. The averaged V1-V8 QRS envelopes were calculated through frequency ranges from 250 to 1000Hz. The DYS was assessed as a difference between soonest and latest activation in V leads. The standard QRSd was also measured. All the ECG parameters were assessed before, just after, and 6 months after the CRT during CRT off. Patients with a relative decrease of 10% and more in end-diastolic volume of left ventricle were considered CRT responders. Results From all 26 patients, in 18 CRT responders there was a significantly lower DYS after 6 month follow-up compared with baseline DYS (-17.0±24ms, p<0.01), while there was no DYS parameter change before and just after the CRT (-1.9±13ms, NS). No significant difference was found in QRSd just after CRT (-1.7±9.1ms, NS) and 6 month follow-up (-8.3±24ms, NS) against the baseline prior CRT. The data from 8 CRT non-responders did not show any significant differences of DYS (-1.0±8ms, NS) or QRSd (0.87±3.2, NS) just after the CRT and 6 month follow-up (-2.8±15ms, NS; 2.6±7.4, NS, respectively) compared to baseline DYS. Conclusion The changes of the DYS parameter show significant shortage of the ventricular conduction delay in CRT responders, whereas the QRSd evinces only a positive trend, but nonsignificant changes. DYS change as a marker of RER corresponds with reverse remodeling assessed by echocardiography.