Atrial fibrillation (AF) can cause heart enlargement and heart failure and can greatly increase the risk of blood clots and strokes. As the atria lose their ability to contract effectively during the property, blood tends to stagnate in the atria, which can then form a blood clot. This thrombus (clot) is dislodged and flows with the blood to the ventricle then enters the cerebral artery branches with the arterial blood, then a cerebral embolism (i.e. stroke) can be formed. If it travels to an extremity, it can cause an arterial embolism in the extremity, requiring amputation in severe cases. The incidence of stroke is six times higher in patients with atrial fibrillation than in normal subjects. The incidence of embolism is even higher in those patients who are older than 65 years old and have a history of stroke, hypertensive disease, diabetes mellitus, and heart failure. Therefore, patients with atrial fibrillation should be treated aggressively. Atrial fibrillation of primary, paroxysmal, and short duration (<2 years) should be treated to restore sinus rhythm as much as possible; permanent atrial fibrillation should be treated with strict anticoagulation and ventricular rate control.