Inclusion Criteria:  Previous embolic stroke with undetermined source with… palpitations with clinical indication for an electrophysiological study (control group) PFO and clinical indication for interventional PFO closure according to current guidelines (intervention group) Sinus rhythm at time of inclusion with no history of AF Planned EP study due to reported palpitations or documented burden of non-sustained atrial arrythymias (>100 atrial ectopic beats /24 hours, atrial tachycardia) Written informed consent  Exclusion Criteria:  previously documented AF indication for therapeutic anticoagulation uncontrolled diabetes mellitus acute coronary syndrom or acute cardiac decompensation within the last 6 months before enrollment enrolled in another study BMI > 40 kg/m² patients who are pregnant of breastfeeding life expectancy < 6 months relevant peripheral artery disease substance abuse