The thyroid is part of the endocrine system and regulates your body's metabolic rate. It is a small gland with a complex job. When the thyroid is not working properly, it can affect many functions of your health including your heart, explains Dr. Robert Smallridge, a Mayo Clinic endocrinologist.

The thyroid is a small butterfly-shaped gland in the front of the neck. It produces a hormone called thyroxine, or T4, that controls virtually every organ system in the body, including the heart.

"It can malfunction either to make too much thyroid hormone—we call that hyperthyroidism. But more commonly, it can become underactive, and that's a condition called hypothyroidism," says Dr. Smallridge.

When thyroid levels are unbalanced in either direction, if can affect cardiovascular functions.

"If someone has low levels of thyroid hormone, cholesterol level goes up. The cholesterol can then have an adverse effect on the heart and peripheral vascular system, and it can lead to an increased risk of heart disease and stroke," says Dr. Smallridge.

Hyperthyroidism on the other hand can increase the risk of atrial fibrillation.

"Hyperthyroidism not only increases the arrhythmia, which increases risk of stroke, it also changes a blood constituent so that the blood becomes more atherogenic and more hypercoagulable so that your risk of thrombotic events increases."

The good news is that the thyroid hormone abnormalities can be managed. It starts with a conversation with your health care provider.