Hyperthyroidism may affect the function of multiple organs throughout the body, including the heart. Rapid heart rate, irregular heart rhythm, and widened pulse pressure are potential heart complications related to hyperthyroidism.

Hyperthyroidism or an overactive thyroid refers to the thyroid gland producing more hormones than the body requires or needs. High levels of thyroid hormones may lead to significant changes in your heart function.

Thyroid hormones, particularly thyroxine (T4) and triiodothyronine (T3), have direct and indirect regulatory effects on your heart cells and vascular tissues.

Some cases of untreated severe hyperthyroidism may increase the risk of heart disease and heart failure by keeping your heart in a high-output state that stretches and weakens the muscle over time. In some instances, untreated hyperthyroidism may be life threatening.

Thyroid hormones affect every organ in your body. When it comes to your heart, these hormones directly regulate the genetic expression and chemical sensitivity of the heart cells and vascular tissues. They also regulate metabolic processes throughout the body that influence the overall demand on your heart.

When elevated thyroid hormones cause symptoms, this is known as thyrotoxicosis, a clinical state of high levels of circulating thyroid hormones.

Thyrotoxicosis promotes changes in the body that affect heart health, such as:

  • faster electrical signaling in heart muscle
  • increased sensitivity to stimulating hormones and neurotransmitters, like adrenaline
  • increased metabolic activity throughout the body
  • dilated blood vessels
  • weakened and stretched cardiac tissue

Over time, hyperthyroidism-related heart symptoms and complications may include:

Hyperthyroidism doesn’t always cause dramatic or alarming heart symptoms, particularly if treated. But common warning signs may include:

  • fast or irregular heart rate
  • dizziness
  • fatigue
  • fainting
  • chest pain or pressure
  • breathlessness
  • anxiety
  • weight loss
  • sleep disturbances
  • tremor

Untreated hyperthyroidism may lead to thyroid storm in rare cases. This is a medical emergency, and symptoms often include:

  • significantly high blood pressure
  • increased heart rate
  • high body temperature

Will everyone with hyperthyroidism experience heart disease?

Not everyone with hyperthyroidism experiences heart disease. Hyperthyroidism occurs across a spectrum of severity, and people with mild or well-managed hyperthyroidism, for example, may not develop any long-term cardiac effects.

Your age, overall heart health, type of hyperthyroidism, and underlying medical conditions can all affect your individual risk.

Heart-related complications of untreated hyperthyroidism

Untreated hyperthyroidism is one potential cause of thyrotoxicosis. When thyroid hormones remain elevated without management, any heart symptoms you’re experiencing can worsen, and some may become irreversible or life threatening.

Approximately 1% of people experiencing thyrotoxicosis progress to thyrotoxic cardiomyopathy, a severe form of dilated cardiomyopathy (DCM) in which the heart muscle (primarily the left ventricle) stretches, becomes thinner and weakens.

DCM is often progressive and prevents your heart from effectively circulating blood. It can create body-wide challenges with blood clots, fluid retention, and organ failure. For many people, it can lead to life threatening arrhythmias by impairing the heart’s ability to contract.

Hyperthyroidism treatment, when indicated, helps reduce the chance of related heart conditions. Treating hyperthyroidism may also reverse some cardiac symptoms before damage is permanent.

Hyperthyroidism can be treated with medications that help regulate thyroid hormone production. Some people with Graves’ disease, an autoimmune condition that causes hyperthyroidism, receive radioactive iodine (RAI) treatment or surgery to remove part or all of the thyroid gland.

In addition to medical management of hyperthyroidism, heart-healthy lifestyle changes may help and include:

  • eating a balanced, whole-food diet low in added salt and sugar
  • being physically active
  • maintaining an optimal weight
  • eliminating or reducing alcohol consumption
  • stopping smoking
  • developing stress management strategies
  • improving your quality and quantity of sleep
  • managing other conditions that may affect your heart health, like diabetes

Elevated thyroid hormone levels in hyperthyroidism can affect heart health in various ways. Blood pressure changes, irregular heart rhythm, rapid heart rate, and increased risk for blood clots are a few examples of possible heart effects of hyperthyroidism.

If left untreated, hyperthyroidism could lead to irreversible damage to your heart and might become life threatening. Depending on your specific case, managing hyperthyroidism may involve medications, RAI, or surgery. These also reduce the chance of heart-related complications.

A heart-healthy lifestyle can also support your overall heart function.