Inclusion Criteria:  Cardiac surgery Signed informed consent by patient or next of kin  Mapping inclusion criteria  NOAF within the first seven postoperative days (168 hours) after cardiac surgery developing on the cardiac surgery ward, intermediate care unit or the intensive care unit of the University Hospital Basel. ICU admission will be set as starting point for observation time.  General Exclusion Criteria:  Preoperative conditions:  History of previous left atrial ablation History of cardioembolic stroke History of amiodarone treatment within three months Any documented history of atrial fibrillation/atrial flutter before surgery Left ventricular ejection fraction <40% Patient included into other study with radiation exposure  Perioperative conditions  Perioperative mechanical circulatory support (e.g., intraaortic balloon pump; extracorporeal membrane oxygenation; left ventricular assist device (e.g. Impella, Abiomed Inc., Aachen, Germany)  Mapping exclusion criteria  Heart rate ≥ 50 bpm AND contraindication to adenosine.  Contraindications to adenosine:  Allergy/intolerance to adenosine History of chronic obstructive pulmonary disease (COPD Gold IV)(28) History of asthma History of Long-QT syndrome Hemodynamically unstable patients (margin of discretion of the attending physician)