Final answer:
Hyperthyroidism is a condition in which the thyroid gland is overactive, causing symptoms such as rapid heartbeat, weight loss, and bulging eyes. Graves' disease is a common cause of hyperthyroidism.
Step-by-step explanation:
Hyperthyroidism is a condition in which the thyroid gland is overactive, resulting in the excessive production of thyroid hormones. This condition is commonly associated with symptoms such as rapid and irregular heartbeat, heat intolerance, weight loss, goiter, and exophthalmia (bulging eyes). One of the most common causes of hyperthyroidism is Graves' disease, which is characterized by the production of thyroid-stimulating immunoglobulin (TSI), leading to an increased metabolic rate and excess body heat.