Inclusion Criteria:

A subject may be enrolled in the study if all of the following inclusion criteria are met:

1. The subject is 18 years of age or older
2. The subject has documented paroxysmal, persistent, or permanent non- valvular atrial fibrillation (i.e., the subject has not been diagnosed with rheumatic mitral valvular heart disease)
3. The subject is eligible for long-term warfarin therapy
4. The subject has a calculated CHADS2 score of 2 or greater; Subjects with a CHADS2 score of 1 may be included if any of the following apply (according to the ACC/AHA/ESC 2006 Guidelines for the Management of Subjects with Atrial Fibrillation subjects requiring warfarin therapy):
   • The subject is a female age 75 or older
   • The subject has a baseline Left Ventricular Ejection Fraction (LVEF) > 30% and < 35%
   • The subject is age 65-74 and has diabetes or coronary artery disease
   • The subject is age 65 or greater and has documented congestive heart failure
5. The subject or legal representative is able to understand and willing to provide written informed consent to participate in the trial
6. The subject is able and willing to return for required follow-up visits and examinations

Exclusion Criteria:

Subjects will be excluded from the study if they meet any of the following criteria:

1. The subject requires long-term warfarin therapy (i.e., even if the device is implanted, the subjects would not be eligible to discontinue warfarin due to other medical conditions requiring chronic warfarin therapy). Additionally, a subject with any of the following is excluded:
   • Thrombosis occurring at a young age (<40 years old)
   • Idiopathic or recurrent venous thromboembolism
   • Thrombosis at an unusual site (i.e., cerebral veins, hepatic veins,renal veins, inferior vena cava, mesenteric veins)
   • Family history of venous thromboembolism or of inherited prothrombotic disorder
   • Recurrence or extension of thrombosis while adequately anticoagulated
2. The subject is contraindicated for warfarin therapy or cannot tolerate long-term warfarin therapy
3. The subject is contraindicated or allergic to aspirin
4. The subject is indicated for antiplatelet therapy other than aspirin (for example, a subject indicated for clopidogrel, prasugrel, ticlopidine or ticagrelor due to DES is excluded from enrollment during the dosing regimen). A subject completing a course of antiplatelet therapy may be enrolled after a 7 day washout period
5. The subject had any interventional or surgical procedure within 30 days prior to enrollment or is planning to have an interventional or surgical procedure in the time between the WATCHMAN device implant and 45-day TEE (e.g., cardioversion, ablation, cataract surgery, dental surgery)
6. The subject had a prior stroke or TIA within the 90 days prior to enrollment
7. The subject has had an MI within 90 days prior to enrollment
8. The subject has a history of atrial septal repair or has an ASD/PFO device
9. The subject has an implanted mechanical valve prosthesis
10. The subject suffers from New York Heart Association Class IV Congestive Heart Failure at the time of enrollment
11. The subject has symptomatic carotid disease (defined as >50% stenosis with symptoms of ipsilateral transient or visual TIA evidenced by amaurosis fugax, ipsilateral hemispheric TIAs or ipsilateral stroke); if subject has a history of carotid stent or endarterectomy the subject is eligible if there is < 50% stenosis
12. The subject's AF is defined by a single occurrence of AF
13. The subject had a transient case of AF (i.e., secondary to CABG, interventional procedure, etc.)
14. The subject's left atrial appendage is obliterated
15. The subject has undergone heart transplantation
16. The subject is currently treated with antibiotics for an active infection
17. The subject has a resting heart rate > 110 bpm
18. The subject has thrombocytopenia (defined as < 70,000 platelets/mm3) or anemia with hemoglobin concentration of < 10 g/dl (i.e., anemia as determined by the investigator which would require transfusion)
19. The subject is actively enrolled in a concurrent clinical study of an investigational drug or investigational device (study specifics may be reviewed with the sponsor prior to enrollment to confirm a concurrent study will not interfere with the outcomes of this study)
20. The subject participated in any of the following studies: PROTECT AF, CAP Registry, or PREVAIL. If the subject received a subject ID number for a prior WATCHMAN study, the subject may not be enrolled. PROTECT AF control subjects may be considered for participation if they have completed 5 year follow up
21. The subject is pregnant or pregnancy is planned during the course of the investigation
22. The subject has a life expectancy of less than two years
23. The subject is unable to complete follow-up visits for the duration of the study

Echo Exclusion Criteria:

A subject is excluded from the study if any of the following echocardiographic exclusion criteria (as assessed via TTE and TEE) are met:

1. The subject has LVEF < 30%
2. The subject has intracardiac thrombus or dense spontaneous echo contrast as visualized by TEE and determined by the echocardiographer within 2 days prior to implant
3. The subject has an existing pericardial effusion > 2mm
4. The subject has a high risk patent foramen ovale (PFO) with an atrial septal aneurysm excursion > 15mm or length > 15mm
5. The subject has a high risk PFO with a large shunt defined as early, within 3 beats or substantial passage of bubbles
6. The subject has significant mitral valve stenosis (i.e., MV <1.5 cm2)
7. The subject has complex atheroma with mobile plaque of the descending aorta or aortic arch
8. The subject has a cardiac tumor