As you already know, atrial fibrillation is one of the most common cardiac arrhythmias and there are many different causes of atrial fibrillation. About 3-5% of all patients with atrial fibrillation have abnormal thyroid function, mainly hyperthyroidism, commonly known as hyperthyroidism. Hyperthyroidism is caused by the synthesis and release of excessive thyroid hormones by the thyroid gland and the secretion of the hormones into the blood, resulting in hyper-metabolism of the body’s physiology. At the same time, thyroid technology and sympathetic excitation are closely related, and an increase in hormones will cause panic attacks, sweating, increased eating and stool intake, and weight loss. If the patient’s hyperthyroidism is not treated in a timely manner and the state of hyperthyroidism is prolonged, some patients also have symptoms such as protruding eyes and eyelid edema. Among the heart diseases associated with hyperthyroidism, atrial fibrillation is a very common one. Hyperthyroidism can cause high cardiac output and low peripheral resistance, which can increase the load on the heart, and thyroid hormones can also cause some electrical remodeling of the atrial muscle, leading to atrial fibrillation. Approximately 10% of atrial fibrillation is clinically caused by hyperthyroidism. Some patients with normal thyroid hormone levels and reduced thyrotropin levels, which we call subclinical hyperthyroidism, also have atrial fibrillation about 5 times more frequently than the normal population. Therefore, even if a patient does not have symptoms of hyperthyroidism, thyrotropin levels should be checked in all patients with atrial fibrillation. Middle-aged patients with hyperthyroidism are generally more likely to have atrial fibrillation, while younger patients are less likely to have atrial fibrillation because of the smaller atria. In middle-aged and older adults, atrial fibrillation is combined with hyperthyroidism. It is necessary to determine whether the cause of atrial fibrillation is related to hyperthyroidism. Because of hyperthyroidism, with aggressive treatment, more than half of patients will spontaneously convert to a normal sinus rhythm if thyroid function returns to normal within 6 weeks. The faster the recovery of thyroid function, the higher the rate of conversion to atrial fibrillation. If atrial fibrillation is clearly caused by hyperthyroidism, the hyperthyroidism must be treated first, along with control of the ventricular rate. If thyroid function returns to normal for a period of time, patients with persistent atrial fibrillation may be considered for pharmacologic control or catheter ablation for atrial fibrillation. However, pharmacologic treatment of AF is usually ineffective when thyroid function is poorly controlled, and catheter ablation is not recommended because of the high recurrence rate.