Both hyperthyroidism and hypothyroidism are abnormalities of thyroid function. Thyroid hormones are important hormones that affect human growth and development and material metabolism. Too much or too little thyroid hormone can affect all systems of the body and produce a variety of hazards. Hyperthyroidism and hypothyroidism can easily become life-threatening in the following cases: i. Complicated heart damage. Both hyperthyroidism and hypothyroidism can cause heart damage, resulting in hyperthyroid heart disease and hypothyroid heart disease, respectively. Hyperthyroidism can lead to arrhythmias such as atrial fibrillation, resulting in heart enlargement, heart failure, etc. In severe cases, cardiac arrest can occur. Hypothyroid heart disease can also lead to slow heart rate, weakened myocardial contraction, pericardial effusion, etc., which can lead to cardiac arrest in severe cases. Second, thyroid crisis and hypothyroidism crisis. When hyperthyroidism is severe, thyroid crisis may occur under the causative factors such as infection, iodine treatment, pregnancy, etc. The mortality rate of thyroid crisis is high. Hypothyroid crisis can also occur in hypothyroid patients with triggers such as vomiting and infections. Hypothyroid crisis is mucinous edema coma, and mucinous edema coma can also endanger the patient’s life. Hypokalemia, hyperthyroidism can be complicated by hypokalemia. Severe hypokalemia can affect the electrophysiological stability of the heart muscle, leading to respiratory and cardiac arrest.