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Lack of response to cardiac resynchronization therapy (CRT) may be due to the presence of significant amount of scar or fibrotic tissue at myocardial level. This study sought to investigate the potential impact of myocardial contractile reserve as assessed during exercise echocardiography on left ventricular (LV) reverse remodelling (decrease in LV end-systolic volume ≥15% after 6 months of CRT).Fifty-one consecutive patients with heart failure underwent exercise Doppler echocardiography before CRT implantation to assess global contractile reserve and local contractile reserve (assessed by two-dimensional speckle tracking) in the region of the LV pacing lead. Responders (30 patients) showed a greater exercise-induced increase in left ventricular ejection fraction (LVEF) compared with non-responders (P < 0.001). Contractile reserve was directly related to the improvement in LVEF and to LV reverse remodelling after 6 months of CRT (P < 0.001). A 6.5% exercise-induced increase in LVEF yielded a sensitivity of 90% and a specificity of 85.7% to predict the response after 6 months of CRT. Baseline myocardial deformation as well as contractile reserve in the LV pacing lead region was greater in responders than in non-responders (P < 0.0001).Myocardial contractile reserve (global and regional) is a strong predictive factor of LV reverse remodelling after CRT.