Hypothyroidism occurs when the thyroid gland produces less of certain hormones than the body needs. Symptoms include fatigue, muscle aches, brittle fingernails and hair, depression, swollen face, joint pain, weight gain and increased sensitivity to cold temperatures.

Hypothyroidism occurs when the thyroid gland produces less of certain hormones than the body needs. Symptoms include fatigue, muscle aches, brittle fingernails and hair, depression, swollen face, joint pain, weight gain and increased sensitivity to cold temperatures. Physicians treat hypothyroidism by giving sufferers synthetic thyroid to restore hormone levels. Left untreated, hypothyroidism may affect the heart in a number of negative ways.

Pericardial effusion, a condition marked by an overabundance of fluid collecting in the sac around the heart, may result from hypothyroidism, reports MayoClinic.com. Inflammation of the pericardium, the name for the sac around the heart, usually causes pericardial effusion. This inflammation may occur due to disease or injury, and it puts pressure on the heart. The heart function decreases and may cause heart failure or death. Healing a pericardial effusion caused by hypothyroidism includes treatment for the thyroid and possibly anti-inflammatory medications or surgery.

Hypothyroidism may cause an enlarged heart. This condition results from an underlying medical problem, like a thyroid problem. An enlarged heart, also called cardiomegaly, may cause no symptoms, but when symptoms present, they include shortness of breath and other breathing difficulties, dizziness, atypical heart rhythm, swelling and cough. Complications from having an enlarged heart generally depend on the underlying cause; the possibility of heart failure from enlargement of the left side of the heart is the most serious risk. Physicians treat an enlarged heart caused by hypothyroidism by restoring normal thyroid function.

Hypothyroidism may result in heart disease. Mucin, a substance found in tissues of the body, accumulates abnormally in the body of someone with hypothyroidism. Mucin attaches to water, which causes swelling in the heart muscle. This results in a weakened heart that may cause both a lowered or increased heart rate as well as heart palpitations. TheHeart.org reports that older adults with severe hypothyroidism and those with high levels of thyroid-stimulating hormone have an increased risk of developing heart failure.