Approximately 100 patients who plan to have pulmonary vein isolation by antral radiofrequency or cryoablation for paroxysmal or persistent atrial fibrillation, or left atrial flutter following prior left atrial ablation procedures, with CHADS2 score of 0-6 or CHADS2-VASc score 0-9 will be eligible for this trial and enrolled. A transesophageal echocardiogram (TEE) will be performed pre-procedure based on the presenting cardiac rhythm the day of planned catheter ablation, stroke risk by CHADS2 or CHADS2-VASc score, and preceding use of therapeutic anti-coagulation (as per current 2012 HRS/ACC/ESC guidelines on atrial fibrillation management). Immediately following the ablation procedure (4-6 hours after sheath pull and vascular hemostasis), dabigatran etexilate 150mg bid, or 75mg twice daily based on creatinine clearance in the Use in Specified Populations (USPI), will be administered for a minimum of 3 months post RF ablation. This represents the standard blanking period for post atrial fibrillation or left atrial flutter catheter ablation anticoagulation therapy. After the 3 months blanking period, patients may safely be taken off dabigatran in the low risk group for stroke or thromboembolism, according to the investigators discretion (CHADS 2 score 0-1, or CHADS2-VASc score 0-1). If on dabigatran etexilate pre-procedure, the drug will be held at least 24 hours before the intervention depending on renal function of the patient (as per recommendations in the USPI). If possible, discontinue dabigatran 1 to 2 days (CrCl >50 mL/min) or 3 to 5 days (CrCl <50 mL/min) before an invasive or surgical procedure, due to increased risk of bleeding.