Can Hypothyroidism Cause Palpitations or a Fast or Slow Heart Rate?

Yes, thyroid problems can change how your heart beats, but low thyroid hormone usually pushes the heart rate down, not up. If you have hypothyroidism or Hashimoto's and feel your heart racing or pounding, the more likely reasons are a dose that has drifted too high, a short overactive phase of Hashimoto's, or something outside the thyroid such as anemia, anxiety or caffeine.

What does thyroid hormone do to your heart rate?

Heart muscle and blood vessels respond directly to thyroid hormone, mainly its active form, T3. With too little, the heart beats more slowly, each beat is weaker, and the heart pumps less blood per minute. With too much, the resting rate rises, the heart pumps harder, and the upper chambers become more prone to irregular rhythms [C1].

That is why "slow heart rate" appears among the signs of hypothyroidism, while racing or irregular beats belong to an overactive thyroid [C2][C3]. A normal resting heart rate is 60 to 100 beats per minute. Above 100 is called tachycardia and below 60 bradycardia, although fit people and people on heart-slowing medicines can sit below 60 without a problem [C3].

Can hypothyroidism cause palpitations?

It can, but less often than people assume. Palpitations mean you are aware of your heartbeat: it feels like it is pounding, racing, fluttering or skipping. The rhythm itself may be normal or abnormal [C3]. What matters is whether the beat is fast at rest, irregular, or comes with other symptoms.

Large studies suggest low thyroid function is not a strong driver of rhythm problems. In a Danish cohort of 586,460 adults, both overt and subclinical hypothyroidism were associated with a lower risk of atrial fibrillation than normal thyroid function [C6]. A pooled analysis of 30,085 people from 11 cohorts found TSH was not significantly linked to new atrial fibrillation in subclinical hypothyroidism [C7].

Why can you feel palpitations if your thyroid is underactive?

Other causes still apply, and some are more common with thyroid disease.

Your dose may be too high. If your levothyroxine dose ends up higher than your body needs, you get symptoms of too much hormone. MedlinePlus lists anxiety, palpitations, rapid weight loss, restlessness, shakiness and sweating as signs to report to your doctor while on replacement [C2]. Only a blood test shows whether this is happening.

A hashitoxicosis phase. Hashimoto's usually moves slowly toward an underactive thyroid, but some people are euthyroid or even hyperthyroid at presentation, and hashitoxicosis is one of its recognized forms [C8]. Inflamed tissue releases stored hormone and the heart can race. Our guide to hashitoxicosis explains how it differs from Graves' disease.

Anemia. Iron deficiency anemia can cause palpitations, tiredness, dizziness and headaches [C9]. Low iron, low B12 and low thyroid hormone often overlap, as explained in anemia in hypothyroidism.

Anxiety and stress. Anxiety, stress and panic are among the most common causes of palpitations [C3]. With Hashimoto's it can be hard to tell whether anxiety comes from shifting thyroid levels or stands on its own.

Caffeine and other stimulants. Too much caffeine can cause a fast heart rate and shakiness. MedlinePlus puts the amount that is not harmful for most adults at up to 400 mg a day, and an 8-ounce cup of coffee carries roughly 95 to 200 mg [C10]. Nicotine, alcohol, decongestants such as pseudoephedrine, diet pills and fever can also trigger palpitations [C3].

A heart rhythm problem. Heart disease, a valve problem such as mitral valve prolapse, low potassium and certain medicines can all cause true rhythm problems [C3], whatever your thyroid is doing.

Heart symptoms and what they may mean

Use this to start a conversation with your doctor, not as a diagnosis.

Heart symptom	Possible thyroid link	Other common causes	What to ask
Slow pulse at rest, with tiredness or feeling cold	Low thyroid hormone or a dose that is too low [C1][C2]	Endurance training, medicines that slow the heart [C3]	"Is my TSH above range? Do I need an ECG?"
Racing or pounding heart while resting	Dose too high, or a hashitoxicosis phase [C2][C8]	Anxiety, caffeine, fever, decongestants, alcohol [C3]	"Could my dose be too high? Can we check TSH and free T4?"
Irregular, chaotic heartbeat	Atrial fibrillation is linked to low or suppressed TSH [C4][C5][C6]	Heart disease, valve problems, low potassium [C3]	"Do I need an ECG or a heart monitor?"
Skipped or extra beats	No specific thyroid link; worth a TSH check if new	Caffeine, nicotine, stress; more than 6 a minute needs prompt review [C3]	"Are these extra beats? How many is too many?"
Palpitations with breathlessness on stairs	Anemia is common with hypothyroidism [C9]	Iron deficiency anemia, heart or lung conditions	"Can we check a blood count and ferritin?"
Hearing your heartbeat in your ear	High-output states such as an overactive thyroid [C1][C11]	Blood vessel and vein causes, raised pressure inside the skull [C11]	"Does this need a hearing check or imaging?"

Does a low TSH or too much levothyroxine raise atrial fibrillation risk?

Atrial fibrillation (AF) is an irregular rhythm of the heart's upper chambers that can lead to stroke and heart failure [C7].

In a Scottish study of 17,684 people on long-term levothyroxine, a fully suppressed TSH (0.03 mU/L or lower) was linked to a 1.6 times higher rate of heart rhythm problems compared with a TSH in range. A low but not suppressed TSH (0.04 to 0.4 mU/L) showed no increase. A TSH above range was also linked to more rhythm problems (1.8 times), so both too little and too much hormone matter [C4]. It was observational, so it shows associations, not cause.

People whose own thyroid makes too much hormone show the same pattern. In a pooled analysis of 10 cohorts, subclinical hyperthyroidism (TSH below 0.45 mIU/L with normal free T4) was associated with a 68% higher AF risk, highest when TSH was below 0.10 mIU/L [C5]. In the Danish cohort, a suppressed TSH carried a 41% higher AF rate [C6]. Even within the normal range, people in the top quarter of free T4 had a 45% higher AF risk than those in the bottom quarter [C7].

More hormone is not automatically better for the heart, as our guide to thyroid and cardiovascular risk explains. Dose decisions belong to your doctor, guided by your TSH and how you feel.

Can hypothyroidism make you short of breath with palpitations?

Low thyroid hormone can weaken breathing muscles and lower exercise tolerance, and in severe cases fluid can collect around the heart or lungs; see shortness of breath in hypothyroidism. When breathlessness and palpitations come together, anemia is worth checking early [C9]. If they start suddenly or at rest, count it as a red flag rather than waiting for your next thyroid test [C3].

Why do I hear my heartbeat in my ear?

A whooshing or thumping in the ear in time with your pulse is called pulsatile tinnitus, unlike the steady ringing of ordinary tinnitus. A cause is found in more than 70% of people after a thorough evaluation, including blood vessel and vein conditions, raised pressure inside the skull, structural ear problems, and body-wide states that raise cardiac output [C11].

An overactive thyroid raises cardiac output [C1], so a dose that is too high or a hashitoxicosis phase is a possible thyroid link. Low thyroid hormone does the opposite, which makes hypothyroidism itself an unlikely cause. Pulsatile tinnitus can sometimes be an early warning of stroke, so it deserves a medical evaluation [C11]. The steady ringing type is covered in tinnitus and Hashimoto's.

What should you track, and which tests might your doctor order?

Note when palpitations start and stop, whether they begin suddenly, whether the beat feels fast, slow, regular or irregular, and what you were doing; doctors ask exactly these questions [C3]. Count your pulse for 30 seconds and double it. Add caffeine, alcohol, sleep, stress, and when you took levothyroxine and supplements. Thyra lets you log symptoms next to medication timing, meals and labs, and looks for patterns once you have 7 or more tracked days. It shows what tends to happen around your palpitations, not why.

Tests your doctor may consider:

• TSH and free T4, to see whether your dose is too high or too low, or a hyperthyroid phase is under way [C4][C8].
• An electrocardiogram (ECG), often the first heart test [C3].
• A Holter monitor for 24 hours or a longer monitor if palpitations come and go, and an echocardiogram if an abnormal rhythm is found [C3].
• A blood count and iron studies if anemia is possible [C9], plus potassium [C3].

When to talk to your doctor or get urgent care

Call emergency services (911 in the U.S.) if palpitations come with chest pain, shortness of breath, fainting, dizziness or lightheadedness, or unusual sweating [C3].

Contact your doctor promptly if palpitations are new or different, if you feel more than 6 extra beats a minute or in groups of 3 or more, if your resting pulse is over 100 without exercise, anxiety or fever, or if you have heart disease or risk factors such as diabetes or high blood pressure [C3]. On thyroid hormone, also report a rapid heartbeat or signs your dose may be too high [C2]. A beat that feels chaotic should be checked with an ECG soon.

Frequently asked questions

Does hypothyroidism cause a fast or slow heart rate?

Usually a slow one. Low thyroid hormone slows the heart and reduces how much blood it pumps [C1], and a slow heart rate is a listed sign of hypothyroidism [C2]. A fast resting rate is more typical of too much hormone.

Can levothyroxine cause palpitations?

Palpitations can be a sign the dose is higher than you need, and MedlinePlus advises telling your doctor if they appear [C2]. Do not change or stop your dose on your own; a TSH and free T4 test shows whether the dose is the likely cause.

Does subclinical hypothyroidism increase atrial fibrillation risk?

The large studies show no clear link. A pooled analysis of 30,085 people found TSH was not significantly associated with new AF in subclinical hypothyroidism [C7], and a Danish cohort found a lower AF risk with hypothyroidism [C6]. The AF signal sits on the low-TSH side.

Is a TSH of 0.1 too low for my heart?

Your doctor sets your target. On levothyroxine, a fully suppressed TSH (0.03 mU/L or lower) was linked to more rhythm problems, while 0.04 to 0.4 mU/L was not [C4]. In people with an overactive thyroid of their own, AF risk was highest below 0.10 mIU/L [C5].

Bottom line

Hypothyroidism on its own tends to slow the heart, so new palpitations are a reason to check whether your dose is too high, whether Hashimoto's is in an overactive phase, and whether anemia, anxiety or caffeine is involved. Keep a simple log, ask your doctor about a TSH, free T4 and an ECG, and get urgent care if palpitations come with chest pain, fainting or shortness of breath.