['QRS duration and morphology are known established predictors of cardiac resynchronisation therapy (CRT) response, whereas mechanical dyssynchrony is not. Our aim was to determine if mechanical dyssynchrony provides independent prognostic information on CRT response.', 'We studied 369 consecutive patients with heart failure (HF) with low ejection fraction (EF) and widened QRS receiving CRT. Radial dyssynchrony (septal-posterior radial peak strain delay ≥130\u2005ms by speckle tracking) assessment was possible in 318 patients (86%). Associations with left ventricular end-systolic volume (LVESV) changes were examined using linear regression, and clinical outcomes analysed using Cox regression adjusted for multiple established outcome correlates.', 'Patients with radial dyssynchrony before CRT (64%) had greater improvements in EF (8.8±9.4 vs 6.1±9.7 units, p=0.04) and LVESV (-30±41 vs -10±30\u2005mL, p<0.01). Radial dyssynchrony was independently associated with reduction in LVESV (regression coefficient -10.5\u2005mL, 95% CI -20.5 to -0.5, p=0.040) as was left bundle-branch block (-17.7\u2005mL, -27.6 to -7.7, p=0.001). Patients with radial dyssynchrony had a 46% lower incidence of death, transplant or implantation of a left ventricular assist device (adjusted HR 0.54, 95% CI 0.31 to 0.92, p=0.02) and a 39% lower incidence of death or HF hospitalisation (0.61, 0.40 to 0.93, p=0.02) over 2\u2005years.'] Is mechanical dyssynchrony additive to ECG criteria and independently associated with reverse remodelling and clinical response to cardiac resynchronisation therapy in patients with advanced heart failure?