The heart is a major target of thyroid hormones. Any change in thyroid hormone levels will be responded to by the heart.

Too little thyroid hormone as a consequence of an underactive thyroid (hypothyroidism):

  • causes your heart to beat too slowly or irregularly, to flutter with missing or additional beats. As a consequence bradycardia may develop; this form of arrhythmia leaves your organs and tissues without enough oxygen and nutrients. Severe bradycardia can result in cardiac arrest.
  • causes your blood pressure to change. Over time, high blood pressure will develop with the consequence of developing atherosclerosis, a risk for heart attack and stroke.
  • causes your cholesterol in the blood to rise and calcification, so called plaque, to develop in your arteries and makes them stiff. All these effects increase the risk for heart attack, heart failure and atherosclerosis.

Too much thyroid hormone as a consequence of an overactive thyroid (hyperthyroidism):

  • causes chest pain and palpitations that are not revealed by a heart check-up
  • causes the heart to beat faster. Tachycardia may develop, a form of arrhythmia that implies the danger of heart attack or death
  • causes the blood pressure to increase. A so called wide pulse pressure can develop with elevated systolic reading and normal diastolic reading. A wide pulse pressure is an important risk factor and predictor of mortality from heart disease, especially from atherosclerosis.


Thyroid disorders are often overlooked or misinterpreted. In Canada, for example, 30% of the population has some form of thyroid disorder. But only 50% of them are diagnosed leaving as much as 50% untreated9. Without treatment an under- or overactive thyroid worsens or accelerates any pre-existing heart disease or causes new ones.


  • Dillmann WH. Thyroid Hormone Influences on the Cardiovascular System: Molecular and Clinical Studies. Thyroid Today 2001; 24 (3+4):1-13
  • Klein I et al. Thyroid disease and the heart. Circulation 2007; 116: 1725-1735
  • ATA Hypothyroidism Booklet. The American Thyroid Association. 2003 Accessed December 2011
  • Benetos A et al. Pulse Pressure – A Predictor of Long-term Cardiovascular Mortality in a French Male Population. Hypertension 1997; 30: 1410-1415
  • About thyroid disease. Thyroid foundation of Canada