Atrial Fibrillation (AF) is a common heart rhythm problem that can be eliminated by a radiofrequency ablation procedure. The purpose of this study is to assess the amount of AF that occurs before and after an ablation procedure associated with symptoms versus AF that is not associated with any symptoms. This study will confirm whether patients' symptoms or lack of symptoms post-ablation correlate well with actual episodes of Atrial Fibrillation. This is important information for physicians to know as it will help guide patient care post-ablation in the future. Information on patients' AF episodes will be collected by an implantable loop recorder (ILR) which will be implanted in all study patients 3 months prior to their AF ablation procedure. The ILR will automatically collect information on detected AF episodes while patients will records any symptoms related to AF episodes in study diaries.

Patients scheduled to undergo a first time ablation for AF will be implanted with an implantable loop recorder (ILR), capable of automatically recording episodes of AF, 3 months prior to their ablation procedure. Patients will also be given a standardized diary in which they will record all perceived episodes of AF. Patients will have the data from the ILR downloaded prior to their ablation to record baseline AF data.

A blanking period of 3 months will be used to censor early recurrences post-ablation. A 'successful' AF ablation will be defined as a lack of AF episodes > 2min at least 3 months post-ablation. A 'Failure' AF ablation will encompass all patients not meeting the definition of 'success'. Redo ablation procedures will be allowed in this protocol for patients who continue to have AF recurrences beyond the first three months post-ablation.

After the patient's ablation procedure, patients will be followed every 3 months for 18 months. At each follow-up visit data on AF episodes from the ILR and the patient diaries will be collected. Patients will be blinded to the data downloaded from the device.

Further data will be collected as the patient study follow-up period has been extended to include a 30-month post-ablation visit with device interrogation as device battery is 36-42 months.

Inclusion Criteria:

• Age > 18 years old.
• First-time ablation procedure for AF.
• Symptomatic AF which has been refractory to at least one antiarrhythmic medication. "Symptomatic" patients should be patients who feel that they are aware of when they are in or out of AF. Symptoms may include palpitations, shortness of breath, chest pain, fatigue, or other symptoms, or any combination of the symptoms listed above.
• Patients must have paroxysmal or persistent AF. Paroxysmal patients should have had at least 4 episodes of AF in the 6 months prior to assessment/ablation. Paroxysmal AF is defined as AF which spontaneously terminates within 7 days. Persistent AF is defined as AF which sustains for longer than 7 days, or AF lasting less than 7 days which requires either pharmacologic or electrical cardioversion.
• At least one episode of AF must have been documented by ECG or Holter within 12 months of inclusion in the study.
• No contraindication to systemic anticoagulation with heparin or coumadin.
• Patients must be able and willing to provide written informed consent to participate in the study.

Exclusion Criteria:

• Patients with permanent atrial fibrillation. Permanent AF is defined as chronic, persisting AF (typically more than 1 year) for which cardioversion (pharmacologic or electrical) has failed or will never be attempted.
• Patients with AF felt to be secondary to an obvious reversible cause.
• Patients with contraindications to systemic anticoagulation with heparin or coumadin.
• Patients who have previously undergone atrial fibrillation ablation.
• Patients who are or may potentially be pregnant.
• Left atrial size > or equal to 55 mm.