The day before implantation of the CRT the following investigations are scheduled: Echocardiography (to asses LV function and dimensions), cardiac CT-scan (to localize all available epicardial veins), myocardial scintigraphy (82Rubidium positron emission tomography (Rb-PET)), to determine the extent and distribution of scar tissue and LVEF (13,14)), blood samples and clinical evaluation.