The aim of the study is to enroll approximately 200 cases from 10 research centers nationwide, completed left atrial appendage occlusion (LAAO) successfully, and give apixaban (5 mg bid) postoperatively.

Inclusion Criteria:

• age between 18 to 85 years;
• understand the purpose of the trial, sign the informed consent form voluntarily
• successful surgery (no pericardial effusion, pericardial tamponade, or device displacement during operation; no pericardial effusion before discharge), meet COST standard during operation.
• In accordance with the indications for left atrial appendage occlusion: CHA2DS2-VAS2 score≥2 points and/or HAS-BLED score≥3 points
• unable or unwilling to take oral anticoagulants
• life expectancy≥1 year

Exclusion Criteria:

• History of previous cardiac surgery (valve disease, cardiomyopathy, severe coronary occlusion);
• Inability to tolerate trans-esophageal echocardiography;
• Preoperative trans-esophageal echocardiography suggests thrombus in left atrial appendage/left atrial;
• Patients with severe renal insufficiency (creatinine clearance rate<15ml/min);
• Patients with liver disease accompanied by abnormal blood coagulation and clinically related bleeding risks;
• Clinically significant active bleeding;
• The baseline platelet count is severely reduced: PLT≤50*10^9/L;
• Severe cardiac insufficiency (preoperative transthoracic echocardiography indicated LVEF <35%; uncontrolled heart failure (NYHA IV))
• Allergy or contraindication to anticoagulant drugs such as aspirin, clopidogrel, apixaban, etc .;
• Serious heart valve disease or other structural abnormalities need do elective surgical treatment; or severe coronary heart disease require limited-term intervention;
• Less than 45kg or more than 100kg.
• Take strong CYP3A4 and P-gp inhibitors (including pyrrole antifungal drugs, HIV protease inhibitors, etc.) for systemic treatment;
• Patients with other diseases besides atrial fibrillation (such as after mechanical valve replacement, spontaneous or recurrent venous thromboembolism, etc.) need anticoagulation treatment;
• Unsuccessful surgery (serious pericardial tamponade, massive bleeding and other life-threatening complications occur within 3 days after left atrial appendage closure);
• Pregnancy or lactation;
• Participating in other uncompleted clinical trials;
• Investigator considers inappropriate subjects.

The study is going to enroll approximately 200 cases who completed left atrial appendage occlusion (LAAO) successfully from 10 research centers nationwide.