Hyperthyroidism can be detected in about 3% of patients with atrial fibrillation seen in the emergency room. Hyperthyroidism, short for hyperthyroidism, is a condition in which the thyroid gland synthesizes and releases too much thyroid hormone, causing hyper-metabolism and sympathetic excitation, resulting in panic attacks, sweating, increased eating and bowel movements, and weight loss. Most patients also have proptosis, eyelid edema, and loss of vision. Atrial fibrillation is a frequent complication of heart disease in patients with hyperthyroidism. Overall, 10% to 30% of atrial fibrillation is caused by hyperthyroidism. Subclinical hyperthyroidism (normal thyroid hormone levels with reduced thyrotropin levels) can also increase the risk of atrial fibrillation fivefold. In a large study of 23,638 patients, the incidence of atrial fibrillation in clinical and subclinical hyperthyroidism was 14% and 13%, respectively, which was significantly higher than the incidence of atrial fibrillation in patients with normal thyroid function, which was 2.3%. Therefore, thyrotropin levels should be checked in all patients with atrial fibrillation, even if they do not have symptoms of hyperthyroidism. Atrial fibrillation due to hyperthyroidism is more common in patients >40 years of age. 20%-25% of elderly patients with hyperthyroidism have atrial fibrillation as a complication, while atrial fibrillation is uncommon in patients under 30 years of age. Many older patients with atrial fibrillation have comorbid hyperthyroidism. It is important to determine whether the etiology of atrial fibrillation is related to hyperthyroidism because within 6 weeks of normalization of thyroid function, 60% of patients will spontaneously convert to sinus rhythm. The faster the recovery of thyroid function, the higher the rate of conversion to atrial fibrillation. When abnormal thyroid function is detected on examination, secondary hyperthyroidism due to amiodarone use in patients with atrial fibrillation needs to be ruled out first. Hyperthyroidism is a common adverse drug reaction to amiodarone, and can occur in addition to the proptosis sign. When patients with atrial fibrillation taking amiodarone develop abnormal thyroid function, it needs to be differentiated from atrial fibrillation caused by hyperthyroidism. If thyroid function gradually returns to normal, consider hyperthyroidism caused by amiodarone and avoid amiodarone in the future. If hyperthyroidism causes atrial fibrillation, treatment of hyperthyroidism is required first. Patients with normalized thyroid function and atrial fibrillation may be considered for drug control or catheter ablation for atrial fibrillation. However, pharmacological treatment of AF is usually ineffective when thyroid function is not well controlled, and catheter ablation is not recommended because of the high recurrence rate.