Your Thyroid And Your Heart

The thyroid hormone is vital for normal cardiovascular function, so when there is over or underproduction of the thyroid hormone, neither the heart nor the blood vessels can function normally. Urban Health speaks to Dr Wong Ming, Consultant Physician and Endocrinologist at Sunway Medical Centre, to better understand how too much or too little thyroid hormones can affect your cardiovascular health:


In hypothyroidism, heart beat is reduced and the heart muscle is weakened in both contraction and relaxation phase. This means that the heart cannot pump as efficiently as it should and therefore the amount of blood it pumps with each heartbeat is reduced. In addition, because the heart muscle is not able to relax normally between heart beats, a condition called diastolic dysfunction may result.


Symptoms can be seen in anyone with hypothyroidism, but someone with an underlying heart disease is more likely to complain. Common symptoms include:

  • Slow heart rate: The heart rate is modulated by the thyroid hormone. In hypothyroidism, the heart rate is 10-20 heartbeats per minute slower than normal.
  • Shortness of breath on exertion and decreased exercise capacity: Hypothyroidism can produce heart failure in patients with relatively mild underlying heart disease and may result in fluid collection around the heart.
  • Swollen legs (Edema): Can occur as a result of heart failure. Hypothyroidism itself can cause a edema known as myxedema. This is caused by an accumulation of abnormal proteins in the fluids external to the body’s cells.
  • Worsening of coronary artery disease: Hypothyroidism causes an increase in LDL (bad cholesterol) which can accelerate any underlying coronary heart disease.

As hypothyroidism can be present subtly, it is important to measure your thyroid hormone levels if you have any of these presentations. People with hypothyroidism should also be treated with tyroxine.


In hyperthyroidism, there is an overproduction of the thyroid hormone which leads to increased heartbeat. It increases the force of contraction and the amount of oxygen that is required by the heart muscle. As a result, the heart becomes overworked.


Again, symptoms can be seen in anyone with hyperthyroidism but it is more problematic in people with an underlying heart disease. Common presentations include:

  • Palpitations: The sensation of the heart beating very fast. This is due to increased heart rate and increased force by which the heart contracts. People with underlying heart disease ca present with abnormal heart rhythm such as atrial fibrillation (irregular and fast heart beat). It is important to rule our hyperthyroidism in the elderly especially if they present with atrial fibrillation with no clear underlying cause.
  • Shortness of breath on exertion: Hyperthyroidism can result in heart failure due to the excess workload on the heart.
  • Chest pains: People with ishaemic heart disease can experience an increase in chest pains or even a heart attack.
  • High systolic blood pressure: The forceful heart contractions can increase blood pressure in your arteries.

If you have any of these symptoms which cannot be readily explained, then thyroid function should be measured. People with hyperthyroidism should be treated with anti-thyroid medication or radioactive iodine. Rarely, surgery is required to treat the condition. Impaired cardiovascular function is usually reversible once thyroid hormone function is normalised.

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