Inclusion Criteria:  ≥ 18 years of age They are candidates for a procedure of PFO closure, whatever the indication (secondary prevention of stroke, platypnoea, decompression illness…). The indication must have been confirmed by a multidisciplinary team as recommended by the Haute Autorité de Santé. They are affiliated to Social Security They have provided a signed written consent form ICM implantation and randomization will occur only in patients with successful PFO closure without any major complications  Exclusion Criteria:  History of atrial fibrillation (paroxysmal, persistent or permanent) Electrocardiographic of ventricular pre-excitation or bundle-branch block (QRS >120ms) Ischemic heart disease Dilated or hypertrophic cardiomyopathy A history of heart failure, severe valvular heart disease, left ventricular dysfunction (ejection fraction <50 percent) A long QT interval or Brugada syndrome The bradycardia-tachycardia syndrome (resting heart rate, ≤50 beats per minute, or repetitive sinoatrial blocks during waking hours) Documentation of previous episodes of second or third-degree atrioventricular block High heart rate at baseline > 100 bmp Renal insufficiency (Glomerular filtration rate estimated by the Cockroft and Gault formula <30ml/min/m2), Previous hypokalemia (potassium level <3 mmol per liter) Suspected or known pregnancy (woman of childbearing potential must undergo a pregnancy test) A known hypersensibility to flecainide or its excipients Contemporaneous enrollment in an interventional clinical trial Intended use of a prohibited medication