Previous experience with cardiac resynchronization therapy (CRT) candidates suggests that selection of these patients can be improved. Current clinical guideline approaches are mainly too unspecific and lead to a high non-responder rate of 30-40%, which causes a burden on health care systems and puts patients at risk of an unnecessary treatment who might benefit more from a conservative approach. Previous work indicated that using the assessment of mechanical dyssynchrony on echocardiography can lower the non-responder rate at least by 50% without compromising sensitivity for detecting amendable patients. The current prospective, randomized, multi-center trial was therefore designed to prove that the characterization of the mechanical properties of the left ventricle can improve patient selection for CRT. Patients will be randomized into one of two study arms: a control study arm with treatment recommendation based on clinical guidelines criteria, or an experimental study arm with treatment recommendation based on the presence of mechanical dyssynchrony. All patients will receive a CRT implantation. In the control study arm, bi-ventricular pacing will be turned on. In the experimental study arm, bi-ventricular pacing will be turned on or off, depending on the presence or absence of mechanical dyssynchrony, respectively. The primary endpoint will be non-inferiority in outcome of a treatment recommendation based on mechanical dyssynchrony, achieved with a lower number of CRT devices implanted, effectively leading to a lower number needed to treat. Outcome measures are the average relative change in continuously measured LVESV per arm and the percentage 'worsened' according to the Packer Clinical Composite Score per arm after 1 year follow-up.