Atrial fibrillation is the most common supraventricular arrhythmia in clinical practice and can occur in organic heart disease or in a minority of patients without organic heart disease. In terms of its incidence increases with age. At present, the prevalence of atrial fibrillation in China is about 0.77% in the population aged 30-85 years, with about 5 million people, and about 60% of patients with atrial fibrillation are not taking any anticoagulant drugs. Warfarin is one of the effective drugs for prevention of cerebral infarction in atrial fibrillation, which requires regular testing of the international normalized ratio (INR) because of significant individualized differences and interactions with other drugs and the risk of bleeding. Domestic warfarin is 2.5mg per tablet and imported warfarin is 3mg per tablet. National people take 2.5mg-3mg daily and adjust the dose with a target INR of 2.0 – 3.0. At the beginning of warfarin treatment, INR should be tested once every 3-5 days, and once every 4 weeks when the dose is relatively fixed, and once a month for patients who have been taking the dose for a period of time with stable testing.