The study will include patients with acute heart failure with reduced left ventricular ejection fraction (<40%) triggered by atrial fibrillation (AF) with a heart rate of >130/min. Patients in cardiogenic shock, critical state, or patients requiring emergent electric cardioversion during the first 2 hours will be excluded. The patients will be randomized (1:1) to a strategy of initial intensive heart rate control using continuous infusion of landiolol and boluses of digoxin vs. standard approach to the rate control without the use of landiolol. All patients will receive recommended pharmacotherapy of acute heart failure (diuretics, nitrates, inotropes in patients with signs of low cardiac output - preferentially milrinone or levosimendan). The patients will undergo hemodynamic monitoring, laboratory testing, evaluation of symptoms, and quantification of lung water content by ultrasound for 48 hours. The study will test a hypothesis whether patients treated with initial intensive heart rate control with the preferential use of landiolol will achieve faster heart rate control, compensation of heart failure, and relief of heart failure symptoms without causing hypotension or deterioration of heart failure.

Procedure:

1. Eligible patients with signed consent will be enrolled.

2. Baseline transthoracic echocardiography, laboratory testing, evaluation of subjective dyspnea, lung water by ultrasound, chest x-ray, hemodynamic monitoring (details below)

3. Randomisation 1:1 to standard therapy vs. intensive heart rate control

4. Two hours of therapy with continous hemodynamic monitoring (blood pressure by arterial line, cardiac output and stroke volume non-invasively by bioreactance)

   1. Standard therapy (oral or intravenous beta-blockers other than landiolol while avoiding hypotension or deterioration of hemodynamics, according to the preference of the physician) with a bolus of 250-500mg of digoxin
   2. Intensive heart rate control with the goal to achieve heart rate <115 during the first the hours, preferentially with continuous infusion of landiolol and a bolus of 250-500mg of digoxin. The dose will be titrated according to the actual heart rate and hemodynamic parameters (blood pressure, cardiac index, stroke volume index). If possible, in both groups, electric cardioversion will be preferentially delayed during the first 2 hours. Both groups will receive standard therapy of acute heart failure (diuretics, inotropes if needed-preferentially milrinone or levosimendan, nitrates..)

5. At 2 hours: evaluation of patients subjective dyspnea (primary clinical endpoint), heart rate (primary endpoint), hearth rhythm and hemodynamics

6. After 2 hours, both groups can be treated according to the preference of the physician.

7. Symptoms, heart rate control, hemodynamics and lung congestion will be reevaluated at 12 and 48 hours

8. The study protocol will end after 48 hours.

Inclusion Criteria:

• acute heart failure with reduced left ventricular ejection (<40%)
• atrial fibrillation with heart rate >130/min lasting presumably >12 hours and presumably contributing to the acute heart failure
• pulmonary congestion detected by auscultation, lung ultrasound or CXR

Exclusion Criteria:

• ongoing type 1. myocardial infarction
• cardiogenic shock
• presumed need for mechanical heart support during the first 48hours of the study
• presumed need for electric cardioversion during the first 2 hours of the study
• medication for heart rate control (beta-blockers, calcium channel blockers, digoxin) or antiarrhythmics introduced <24 hours before the study. Chronic therapy with these will not be a contraindication for the study
• thyreotoxicosis