Trial on the effect of biventricUlar pacinG in patients with bradycardia prEserved LV functioN, with the aim of Decreasing Heart failure and ATrial fibrillation.

INTERVENTION: 1. The study contains 120 patients randomized into right ventricular and biventricular pacing group with cross‐over switch of pacing modes after six months 2. Standard descriptive statistics will be used for the analysis, continuous paremeters as age, weight, body mass index were described by median and fifth and ninety‐fifth percentile, occurence of categorical parameters was described by their count and percentages. CONDITION: AV block, Sick Sinus Syndrome ‐ Bradycardia form ; Circulatory System ; Sick Sinus Syndrome PRIMARY OUTCOME: 1. Electrocardiographic parameters (ECG); 2. Echocardiographic parameters (LV Ejection Fraction); 3. Evaluation of NYHA class; 4. Evaluation of Quality of Live (Minnesota Living with Heart Failure questionnaire) SECONDARY OUTCOME: Atrial Fibrillation burden hospitalization for Heart Failure complication of pacing INCLUSION CRITERIA: 1. Bradycardia pacing indication 2. Subject has stable medication (nitrates, diuretics, betablockers) within the last 3 months 3. Echocardiographic exclusion of ventricular (inter‐and intra) dyssynchrony 4. Willing and able to comply with the Clinical investigation Plan 5. Signed Informed consent form 6. Aavailability for follow‐up visits