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Background: Cardiac resynchronization therapy (CRT) is an effective treatment of heart failure (HF) with ventricular dyssynchrony, but not all patients respond to a similar extent. We investigated the efficacy and safety of exercise training (ET) in patients without response to CRT. Methods and Results: Thirty-four patients who participated in a 3-month ET program and underwent cardiopulmonary exercise testing at baseline and after the program were divided into 17 responders and 17 non-responders based on echocardiographic response criteria: either an increase in ejection fraction (EF) ≥10% or a reduction in left ventricular (LV) end-systolic volume ≥10%. Baseline characteristics including peak oxygen uptake (V̇O2) and isometric knee extensor muscle strength (IKEMS) were similar in both groups, but non-responders had lower EF and larger LV. During the ET program, neither group had exercise-related adverse event including life-threatening ventricular arrhythmia. Peak V̇O2 and IKEMS were significantly improved in both groups and there was no significant difference in change in peak V̇O2 or IKEMS between responders and non-responders. On multiple regression analysis, change in IKEMS was an independent predictor of change in peak V̇O2, whereas the response to CRT was not. Conclusions: In HF patients undergoing CRT implantation, ET safely improved exercise capacity regardless of response to CRT, suggesting that even advanced HF patients without response to CRT can possibly benefit from ET.