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Background: We investigated whether reversed electrical remodeling (RER), defined as narrowing of the native electrocardiographic QRS duration after cardiac resynchronization therapy (CRT), might predict prognosis and improvement in echocardiographic outcomes., Methods and Results: A total of 110 CRT recipients were retrospectively analyzed for the end points of death and hospitalization during 18 ± 3 months. Native QRS durations were recorded at baseline and 6 months after CRT (when pacing was switched off to obtain an electrocardiogram) to determine RER. CRT response and mitral regurgitation (MR) improvement were defined as ≥15% reduction in left ventricular end-systolic volume and absolute reduction in regurgitant volume (RegV) at 6 months, respectively. Overall, 48 patients (44%) had RER, which was associated with functional improvement (77% vs 34%; P < .001) and CRT response (81% vs 52%; P < .001) compared with those without RER. The change in the intrinsic QRS duration correlated with the reduction in RegV (r = 0.51; P < .001) and in tenting area (r = 0.34; P < .001). RER was a predictor of MR improvement (P = .023), survival (P = .043), and event-free survival (P = .028) according to multivariate analyses., Conclusions: Narrowing of the intrinsic QRS duration is associated with functional and echocardiographic CRT response, reduction in MR, and favorable prognosis after CRT., (Copyright © 2016 Elsevier Inc. All rights reserved.)