---
title: The heart in thyrotoxicosis
description: How too much thyroid hormone affects the heart, why thyrotoxicosis speeds up the pulse and can cause atrial fibrillation, how this is investigated, which treatment approaches clinical guidelines describe, and when to call an ambulance.
type: disease
preset: sinus-tachycardia
morePresets: [atrial-fibrillation]
aliases:
  - thyrotoxicosis
  - hyperthyroidism
  - thyrotoxic heart disease
  - hyperthyroid heart disease
  - thyrotoxic cardiomyopathy
  - Graves disease
  - Graves' disease
  - diffuse toxic goitre
  - thyroid storm
sources:
  - tier: guideline
    org: minzdrav-rf
    title: Тиреотоксикоз с диффузным зобом (болезнь Грейвса), узловым/многоузловым зобом
    year: 2025
    url: https://cr.minzdrav.gov.ru/view-cr/270_2
  - tier: guideline
    org: esc
    title: 2024 ESC Guidelines for the management of atrial fibrillation developed in collaboration with EACTS
    year: 2024
    doi: 10.1093/eurheartj/ehae176
    url: https://doi.org/10.1093/eurheartj/ehae176
  - tier: guideline
    org: minzdrav-rf
    title: Фибрилляция и трепетание предсердий
    year: 2025
    doi: 10.15829/1560-4071-2025-6668
    url: https://cr.minzdrav.gov.ru/view-cr/382_2
  - tier: reference
    org: msd-manuals
    title: Hyperthyroidism (Thyrotoxicosis, including Graves Disease) (MSD Manual Professional Version)
    year: 2026
    url: https://www.msdmanuals.com/professional/endocrine-and-metabolic-disorders/thyroid-disorders/hyperthyroidism
  - tier: reference
    org: msd-manuals
    title: Hyperthyroidism (MSD Manual Consumer Version)
    year: 2026
    url: https://www.msdmanuals.com/home/hormonal-and-metabolic-disorders/thyroid-gland-disorders/hyperthyroidism
sources_checked: 2026-10-14
review: null
---

Thyrotoxicosis is a condition in which the blood contains too much thyroid hormone, and the hormone has a toxic, harmful effect on organs and tissues.<Cite n={1} /> One of the main targets is the heart: the pulse speeds up, and the most important complication is [atrial fibrillation](../atrial-fibrillation/).<Cite n={1} /> Thyrotoxicosis is one of the causes of rhythm problems that can be found and corrected, which is why thyroid function is always checked in atrial fibrillation.<Cite n={[2, 3]} />

<Diagram name="thyrotoxic-heart-disease">
  <p slot="normal">
    The diagram shows the thyroid gland and the heart. Thyroid hormones affect many body functions,
    including the heart rate.<Cite n={5} /> When the blood holds the usual amount of these hormones,
    the heart beats at its usual rhythm.<Cite n={[1, 5]} />
  </p>
  <p slot="disease">
    In thyrotoxicosis the blood contains too much thyroid hormone, and in most people the gland
    itself is enlarged (a goitre).<Cite n={[1, 5]} /> The heart works under extra load even at rest
    and beats faster.<Cite n={[1, 4]} /> In some patients the atria go into fibrillation, the most
    important heart complication.<Cite n={1} />
  </p>
</Diagram>

## Why it happens

<Patient>

Most often the thyroid gland itself makes too much hormone: in Graves disease (diffuse toxic goitre) or because of nodules in the gland.<Cite n={1} /> Graves disease is an autoimmune disease: the body makes antibodies that drive the gland.<Cite n={1} /> Where food contains little iodine, a common cause is nodules that work on their own.<Cite n={1} /> Thyrotoxicosis can also come from an overdose of thyroid hormone medicines, or from too much iodine, including iodine from medicines that contain it.<Cite n={[1, 4]} />

Too much thyroid hormone makes the heart work under extra load even at rest.<Cite n={1} /> Many symptoms, such as palpitations, nervousness and sweating, happen because the body reacts more strongly to adrenaline and similar hormones.<Cite n={4} />

</Patient>

<Student>

Thyrotoxicosis is a syndrome caused by an excess of thyroid hormones in the blood and their toxic effect on organs and tissues.<Cite n={1} /> Endogenous hyperthyroidism is most often caused by Graves disease, in which stimulating antibodies to the TSH receptor are produced, or by thyroid nodules; in iodine-deficient areas the leading cause is functional autonomy of nodules.<Cite n={1} /> An exogenous cause is overdose of thyroid hormone preparations; excess iodine, including from iodine-containing drugs and iodinated contrast agents, also causes hyperthyroidism, most often in patients with underlying nontoxic nodular goitre.<Cite n={[1, 4]} />

In thyrotoxicosis the myocardium is hyperfunctioning already at rest; the rise in heart rate and myocardial oxygen demand can unmask latent angina and lead to decompensated heart failure.<Cite n={1} /> ESC: clinical and subclinical hyperthyroidism (as well as subclinical hypothyroidism) are associated with an increased risk of AF; in hyperthyroidism, and even in the euthyroid range, the risk of AF increases with lower TSH and higher thyroxine levels.<Cite n={2} />

</Student>

## Symptoms

<Patient>

People with thyrotoxicosis report palpitations, an irregular heartbeat, breathlessness, weakness, sweating, trembling, weight loss, restlessness and poor sleep.<Cite n={1} /> On examination the doctor finds a fast pulse and sometimes raised systolic (upper) blood pressure, a heart murmur or the irregular rhythm of atrial fibrillation.<Cite n={[1, 4]} />

Atrial fibrillation is the most important heart complication; it is more common in older people and in those who already had heart disease.<Cite n={1} /> It can appear even in subclinical thyrotoxicosis, when only TSH is low and the thyroid hormones are still normal.<Cite n={1} /> At first atrial fibrillation usually comes in episodes, and if thyrotoxicosis continues it can become permanent.<Cite n={1} /> It raises the risk of blood clots travelling in the blood vessels (thromboembolism), especially to the brain, which means stroke.<Cite n={1} />

If thyrotoxicosis lasts a long time, the heart can stretch and weaken, and signs of [heart failure](../heart-failure/) appear.<Cite n={1} />

In older people thyrotoxicosis may look unusual: there are few typical signs, and atrial fibrillation, fainting, confusion, heart failure and weakness come to the fore.<Cite n={4} />

</Patient>

<Student>

According to the Russian Ministry of Health thyrotoxicosis guideline, examination reveals tachycardia, widened pulse pressure, a systolic murmur, systolic hypertension and atrial fibrillation.<Cite n={1} /> AF is the most clinically important arrhythmia; it develops more often in older patients and in those with pre-existing structural heart disease, and its likelihood depends directly on the severity and duration of thyrotoxicosis. Atrial flutter is rare; extrasystoles and paroxysmal tachycardia also occur.<Cite n={1} /> AF develops not only in overt but also in subclinical thyrotoxicosis, especially with coexisting cardiovascular disease.<Cite n={1} />

Long-standing thyrotoxicosis can lead to dilated cardiomyopathy with reduced cardiac functional reserve and symptoms of heart failure; once euthyroidism is reached the reserve improves but does not return to the original level.<Cite n={1} /> Subclinical thyrotoxicosis, especially with deeply suppressed TSH, is associated with an increased risk of death from coronary heart disease, AF and heart failure.<Cite n={1} /> Thyrotoxicosis with AF, heart failure or thromboembolism is classed as complicated.<Cite n={1} /> Older patients may present with apathetic or masked hyperthyroidism.<Cite n={4} />

</Student>

<HeartModel highlight={['right-atrium', 'left-atrium']} />

## How it is diagnosed

<Patient>

Thyrotoxicosis is confirmed with a blood test. First the level of thyroid-stimulating hormone (TSH) is measured: the pituitary gland makes it to control the thyroid, and in thyrotoxicosis it is low.<Cite n={[1, 5]} /> Then the thyroid hormones themselves are measured, and to find the cause, for example, the antibodies typical of Graves disease.<Cite n={1} />

Everyone with thyrotoxicosis has an ECG to check the heart.<Cite n={1} /> People with rhythm problems, atrial fibrillation, extra beats (extrasystoles) or heart failure need to see a cardiologist.<Cite n={1} />

It also works the other way round: a person comes with atrial fibrillation, and the cause turns out to be the thyroid. This is why everyone with newly found or recurring atrial fibrillation has a TSH test.<Cite n={[2, 3]} />

</Patient>

<Student>

The initial screening test in suspected thyrotoxicosis is TSH; if TSH is low, free T4 and free T3 are measured; TSH receptor antibodies are a specific biomarker of Graves disease.<Cite n={1} /> Cut-off values are not given here. A resting ECG is recommended for everyone with diagnosed thyrotoxicosis to screen for cardiovascular disease.<Cite n={1} />

ESC 2024: patients presenting with new-onset or recurrent AF should be tested for TSH.<Cite n={2} /> The Russian Ministry of Health atrial fibrillation guideline recommends a TSH test for all patients with AF or atrial flutter as part of the initial work-up and lists thyrotoxicosis among the reversible factors to look for.<Cite n={3} />

</Student>

## How it is treated

<Patient>

The main thing is to treat the thyrotoxicosis itself. There are three approaches: medicines that suppress the thyroid, surgery and radioactive iodine treatment.<Cite n={1} /> The doctor decides which approach to use; severe heart complications, together with other features, are one of the reasons against many years of treatment with tablets alone.<Cite n={1} />

Until the hormone levels are back to normal, a fast pulse is slowed with beta-blockers.<Cite n={1} /> They ease palpitations but do not reduce hormone production.<Cite n={5} /> If beta-blockers cannot be used, the doctor may prescribe certain calcium channel blockers.<Cite n={[3, 4]} /> Whether medicines against blood clots are needed in atrial fibrillation is also decided by the doctor.<Cite n={1} />

Once the hormone levels are normal, sinus rhythm usually returns on its own; less often if the heart was already diseased or the fibrillation has lasted a long time.<Cite n={1} /> Treating the thyroid disease can also lower the risk of stroke.<Cite n={2} /> Until the hormone levels are normal, it is advised to limit physical exertion and stop smoking.<Cite n={1} /> People with heart involvement and rhythm problems should be followed up by a cardiologist or a general physician.<Cite n={1} /> Do not start, stop or change medicines on your own.

</Patient>

<Student>

Treatment options for thyrotoxicosis are medical (antithyroid drugs, or thyrostatics), surgical and radioiodine therapy.<Cite n={1} /> Long-term medical therapy is in most cases not appropriate in certain groups, in particular with severe complications of thyrotoxicosis (AF, heart failure) combined with other features.<Cite n={1} /> Beta-blockers are recommended in thyrotoxicosis with tachycardia until euthyroidism is reached, and often for longer.<Cite n={1} /> Specific drugs and doses are not given here.

Russian Ministry of Health atrial fibrillation guideline: for ventricular rate control in AF with thyrotoxicosis, beta-blockers unless contraindicated; if they cannot be used, selective calcium channel blockers with a direct action on the heart; if rhythm control is desired, thyroid function should be normalised before cardioversion, otherwise recurrence is likely.<Cite n={3} /> An iodine-containing antiarrhythmic drug causes thyroid dysfunction, both hypo- and hyperthyroidism, in 15–20% of treated patients; ESC allows it in hyperthyroidism only if there is no other option, and the Russian Ministry of Health atrial fibrillation guideline considers it contraindicated when the thyroid is overactive.<Cite n={[2, 3, 4]} /> The risk of stroke is higher in hyperthyroidism and can be mitigated by treating the thyroid disorder.<Cite n={2} />

</Student>

## When to call an ambulance

A rare but life-threatening complication is thyroid storm: a sudden severe flare of thyrotoxicosis that is treated in intensive care.<Cite n={[1, 4, 5]} /> Its signs are a high temperature, a very fast pulse, rhythm disturbances, extreme weakness, agitation, and confusion or reduced consciousness.<Cite n={[1, 5]} /> This condition is life-threatening and needs rapid diagnosis and emergency treatment.<Cite n={[1, 4]} /> If a person with known or suspected thyrotoxicosis has these signs, call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK).

Atrial fibrillation, heart failure and thromboembolism in thyrotoxicosis are reasons for emergency admission to hospital.<Cite n={1} /> In atrial fibrillation an ambulance is also called for signs of stroke: see the article on [atrial fibrillation](../atrial-fibrillation/); for sudden severe breathlessness, see the article on [heart failure](../heart-failure/). As with any heart condition, call an ambulance for fainting, chest pain or severe breathlessness: this is the site's general safety rule, repeated at the bottom of every page.

<Quiz />