Inclusion Criteria:  Permanent atrial fibrillation At least one episode of hospitalisation due to heart failure in the previous 12 months. Left ventricular ejection fraction > 40% Average resting heart rate ≤ 110 beats per minute NT-proBNP ≥ 900 pg/ml in the 30 days prior to enrollment Age ≥ 18 years Capacity to understand the nature of the study, legal ability and willingness to give informed consent.  Exclusion Criteria:  Severe frailty (Clinical Frailty Scale ≥ 7) or comorbidity reducing life expectancy to < 12 months. Acute heart failure at the time of enrollment or systolic blood pressure < 80 mmHg in the absence of inotropic agents. Severe chronic kidney disease (estimated Glomerular Filtration Rate ≤ 20 ml/1,73 m2 Severe mitral or aortic valvular heart disease Anaemia (Haemoglobin < 10 g/dl) Morbid obesity (BMI ≥ 35) Severe Chronic Obstructive Pulmonary Disease (Gold ≥ 3) Presence of a different indication for pacing of implantable cardioverter-defibrillator (ICD) Obstructive hypertrophic cardiomyopathy Infiltrative cardiomyopathy (amyloidosis, sarcoidosis, Fabry disease, others) Simultaneous participation in a different trial