Cardiac resynchronization therapy (CRT) has emerged as an established therapy for patients with end-stage heart failure (HF) and symptoms refractory to optimal medication. Resynchronization of the ventricles leads to reduced functional mitral regurgitation (MR) both acutely and chronically and to a better haemodynamic and energetic profile. In addition, large clinical trials have confirmed its beneficial effect on exercise performance and quality of life. The link between the pathophysiological mechanisms of CRT and its positive effect on clinical status has not been fully elucidated. Therefore, this review will focus on the effect of CRT on the haemodynamic role of functional MR and its impact on exercise performance in patients with chronic HF.