The thyroid is a small, butterfly-shaped gland in the front of your neck that makes two thyroid hormones: thyroxine and triiodothyronine. Thyroid hormones control how the body uses energy, so they affect nearly every organ in your body, even your heart. Health care professionals use thyroid tests to check how well your thyroid is working and to find the cause of problems such as hyperthyroidism or hypothyroidism.