24 hour Holter monitoring (24HM) is commonly used to assess cardiac rhythm after surgical therapy of atrial fibrillation. This "snapshot" rhythm documentation leaves a large diagnostic window of non recorded atrial arrhythmias and as such a large amount of uncertainty in follow-up result assessment. To improve accuracy of rhythm surveillance thus gaining a more "real-life" scenario of post surgical ablation therapy cardiac rhythm a new insertable cardiac rhythm monitor device (Reveal® XT 9525, Medtronic Inc., Minneapolis, MN, USA) with full observational continuous heart rhythm documentation is implanted.

In order to verify different follow-up strategies after surgical atrial fibrillation therapy, a comparison of different follow-up scenarios (symptoms, different cardiac documentation devices i.e. ECG and 24 hour Holter monitor, at different follow-up time points) is performed intraindividually. Thus the reliability of these devices and follow-up strategies to define success after ablation therapy is evaluated.

Inclusion Criteria:

• patients in atrial fibrillation (AF duration >4 months)being scheduled for cardiac surgery
• patients with lone atrial fibrillation being scheduled for surgical AF treatment

Exclusion Criteria:

• failure to provide informed consent
• current participation in another clinical trial
• organic cause of atrial fibrillation (hyperthyroidism etc.)

patients who are scheduled for cardiac surgery and who also present with any kind of atrial fibrillation.