The exact severity of atrial fibrillation is determined by the specific condition. Patients can remain asymptomatic for a long time or develop serious conditions such as ventricular arrhythmias, acute heart failure, and thromboembolism. Patients with atrial fibrillation have a generally normal heart rate and are asymptomatic for a long period of time, and thus some patients are found to have atrial fibrillation during a physical examination. This condition is relatively mild in severity, but carries a risk of thromboembolism. If the ventricular rate of a patient with AF exceeds 150 beats per minute, relatively serious conditions such as angina due to myocardial ischemia, dyspnea due to acute heart failure, or pulmonary edema can occur. Prolonged atrial fibrillation may develop into ventricular arrhythmia patients may experience hypotension, fatigue, and in severe cases may even cause cardiogenic shock. In addition, patients with atrial fibrillation are often associated with atrial appendage thrombi. The dislodged thrombus enters the circulation with the arterial blood and can easily cause thromboembolism, such as cerebral embolism, superior mesenteric artery embolism, limb embolism, etc. Cerebral embolism is the most serious. Cerebral embolism is the most serious and may cause hemiplegia or even death. Atrial fibrillation has many dangers, so it is recommended to seek medical treatment in time and follow the doctor’s instructions to avoid aggravation of the condition.