Inclusion Criteria:

• 1. Patients aged 75 years or older, or patients aged at least 70 years with one or more of the following risk factors at baseline:

  • Hypertension (taking antihypertensive drugs of at least two different classes)
  • Diabetes
  • Prior cerebrovascular accident (stroke or transient ischemic attack) or systemic embolism
  • Left atrium diameter greater than or equal to 50 mm by echocardiography
  • Left ventricular ejection fraction less than 0.40 by 2D-echocardiography.
• 2. Availability of one ECG within the last 6 months, showing that the patient was or is in AF/AFL
• 3. Availability of one ECG within the last 6 months, showing that the patient was or is in sinus rhythm.

Exclusion Criteria:

General criteria:

• E1. Refusal or inability to give informed consent to participate in the study.
• E2. Any non cardiovascular illness or disorder that could preclude participation or severely limit survival including cancer with metastasis and organ transplantation requiring immune suppression
• E3. Pregnant women (pregnancy test must be negative) or women of childbearing potential not on adequate birth control: only women with a highly effective method of contraception [oral contraception or intra-uterine device (IUD)] or sterile can be randomized.
• E4. Breastfeeding women
• E5. Previous (2 preceding months) or current participation in another clinical trial with an investigational drug (under development) or with an investigational device.
• E6. Previous participation in this trial.

Criteria Related to a cardiac condition:

• E7. Patients in permanent atrial fibrillation
• E8. Patients in unstable hemodynamic condition such as acute pulmonary edema within 12 hours prior to start of study medication; cardiogenic shock; treatment with IV pressor agents; patients on respirator; congestive heart failure of stage NYHA IV within the last 4 weeks; uncorrected, hemodynamically significant primary obstructive valvular disease; hemodynamically significant obstructive cardiomyopathy; a cardiac operation or revascularization procedure within 4 weeks preceding randomization
• E9. Planned major non-cardiac or cardiac surgery or procedures including surgery for valvular heart disease, coronary artery bypass graft (CABG) , percutaneous coronary intervention (PCI) , or on urgent cardiac transplantation list
• E10. Acute myocarditis or constrictive pericarditis
• E11. Bradycardia < 50 bpm and/or PR-interval > 0.28 sec on the last 12-lead ECG.
• E12. Significant sinus node disease (documented pause of 3 seconds or more) or 2nd or 3rd degree atrioventricular block (AV-block) unless treated with a pacemaker.

Criteria Related to Concomitant Medications:

• E13. Need of a concomitant medication that is prohibited in this trial, including the requirement for Vaughan Williams Class I and III anti-arrhythmic drugs, that would preclude the use of study drug during the planned study period - see Section 8.9.1.

Criteria Related to Laboratory Abnormalities:

• E14. Plasma potassium < 3.5 mmol/l (as anti-arrhythmic drugs can be arrhythmogenic in patients with hypokalemia, this must be corrected prior to randomization).
• E15. A calculated GFR at baseline <10 ml/min using the Cockroft Gault formula