T3 and T4 are abbreviations for two different thyroid hormones in the body, both of which are elevated to indicate that the patient is experiencing thyrotoxicosis. Causes of thyrotoxicosis include hyperthyroidism and thyroiditis. Hyperthyroidism refers to a group of clinical syndromes in which excessive secretion of thyroid hormones in the bloodstream causes increased sympathetic excitability and hyper-metabolism in the body, with the main manifestations being agitation, palpitations, fatigue, fear of heat, weight loss, hyper-appetite, diarrhea, thickened neck and rapid heart rate. Hyperthyroidism is treated by oral medication, iodine-131 therapy and surgery. Patients with hyperthyroidism have a good prognosis after timely and standardized treatment. However, if hyperthyroidism is not detected and treated in a timely manner, the disease may progress and lead to multi-organ involvement, with the most obvious involvement of the heart, which may lead to hyperthyroid heart disease or thyroid crisis due to high thyroid hormone levels. Both hyperthyroid heart disease and thyroid crisis can lead to death in severe cases, so patients with hyperthyroidism should receive standardized treatment and regular review. In the case of thyroiditis, the inflammatory damage causes transient hyperthyroidism, which usually does not require anti-hyperthyroid medication.