Safety and Performance Aspects of CRT-DX System in Patients With Sinus Rhythm

Inclusion Criteria: * Patient is able to understand the nature of study and has provided written informed consent. * Patient is willing and able to perform all follow up visits at the study site. * Patient is willing and able to use the CardioMessenger® and accepts the BIOTRONIK Home Monitoring® concept. * CRT-D is indicated according to the current ESC guidelines. * De novo implantation with no pre-existing defibrillator or pacemaker system * Patient is in sinus rhythm without history of persistent or permanent atrial fibrillation. * Patient has no atrioventricular (AV) block II or III. * Patient has no evidence of impaired sinus node function. * Patient has no need for atrial stimulation, has a resting heart rate (HR) \> 40 b.p.m and achieves a peak HR ≥100 b.p.m even under intended dosage of HR lowering medication verified by an appropriate method as clinical routine examination within 3 months prior to enrollment * NYHA class II or III * Patient receives guideline-based optimized medical therapy for HF including heart-rate lowering medication at the time of enrollment Exclusion Criteria: * Patient is pregnant or breast feeding. * Patient is less than 18 years old. * Patient is participating in an interventional clinical investigation. * Life-expectancy is less than 1 year. * Patient has tachycardia-bradycardia syndrome * Any standard contraindication for CRT-D * Frequent premature ventricular contractions (PVC rate \> 5 %/h) examined within 3 months prior to enrollment by appropriate routine method (e.g. 24 h holter electrocardiogram)