The Department of Cardiology, Aarhus University Hospital, have the capacity and equipment to conduct this trial. The group of investigators contributes with a deep and long-lasting experience in CRT-treatment and 150 de-novo CRT-devices are annually implanted at our institution. We plan to enroll the patients during a two and a half-year period. This study is planned to start in February 2015 as a PhD program for Charlotte Stephansen, MD. Charlotte Stephansen will be the prime investigator in charge of including the patients and she will perform all clinical evaluations and image acquisitions during the admission for CRT implantation and at the six month follow-up. She will also be in charge of analyzing data after study completion.