Heart palpitations and your thyroid: the TSH and T4 link

Heart palpitations and your thyroid are more directly connected than most people think: thyroid hormone acts straight on your heart muscle and rhythm. If your thyroid runs fast, your heart rate rises, at rest too. Two values, TSH and free T4, show whether this applies to you.

Of all the causes of palpitations, I find this the most underrated one. Not because it's the most common, but because it's so measurable and still often checked late.

How does your thyroid cause heart palpitations?

Thyroid hormone is the accelerator of your metabolism, and your heart listens to it directly. More hormone means a higher heart rate, a stronger contraction and a more irritable rhythm. That's why palpitations are among the classic signs of an overactive thyroid (hyperthyroidism).

This isn't a fringe effect. In the standard paper on thyroid and heart, Klein and Ojamaa describe a persistently fast heartbeat in most people with a clearly overactive thyroid, with 5 to 15 percent even developing atrial fibrillation (NEJM, 2001).

The pattern is recognisable. Think of a resting heart rate stuck above 90, poor sleep, always feeling hot, trembling hands and losing weight while eating normally.

Take an account manager of 38 who watches her smartwatch creep from 62 to 85 beats at rest over three months. She sleeps badly, opens the window at night while her partner grabs a jumper, and has lost two kilos without trying. Separately none of those things says much; together they form exactly the list where you want to know your TSH.

Which thyroid values should you check for palpitations?

The two core values are TSH and free T4. TSH is the control signal from your brain, free T4 the hormone your thyroid actually delivers. The combination of the two points in a direction, which makes this one of the most measurable explanations for palpitations.

Read the table as direction, not diagnosis. Interpreting your personal result, reference ranges included, belongs with a doctor.

An interesting detail from the literature: the subclinical variant (low TSH, normal free T4) is also associated with a higher risk of rhythm problems. So you can feel "just a bit restless" while your values are already pointing somewhere.

Can a slow thyroid also cause palpitations?

Yes, though it works differently. With an underactive thyroid your heart rate usually drops, but some people then feel every beat land more heavily, sometimes with a sense of skipped beats. Fatigue, feeling cold and weight gain sit in that same list.

If you mainly feel a heavy, thudding heartbeat without a high tempo, also read the article on a pounding heart at rest. And if you're unsure between fast and slow, the overview of thyroid problems and TSH, T3 and T4 explains how the values relate.

Which other values add context?

Beyond TSH and free T4, a few extra values can sharpen the picture: haemoglobin (anaemia causes similar symptoms), potassium and magnesium (electrolytes influence your rhythm) and glucose. That stops you from running down one track while the explanation sits elsewhere.

If you want to measure this directly, the thyroid function test covers TSH and free T4, no referral needed and reviewed by a doctor. A visit to one of the 700+ draw locations takes about fifteen minutes.

When should you see your GP about palpitations and thyroid symptoms?

See your GP if palpitations come together with weight loss, trembling, heavy sweating, feeling wired or a resting heart rate that stays high. A persistent irregular, chaotic heartbeat always deserves assessment, certainly combined with an abnormal thyroid result; the Dutch GP site Thuisarts draws the same line.

Bring your results to the appointment. With a TSH and free T4 in hand, a GP can ask far sharper questions and refer you if needed.

My concrete next step: if you've had palpitations at rest for more than two weeks, measure your TSH and free T4 and put the result next to your symptom list. Then your GP talks facts instead of hunches.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

References

• Klein I, Ojamaa K. Thyroid hormone and the cardiovascular system. New England Journal of Medicine. 2001. PMID: 11172193.
• Weber BE, Kapoor WN. Evaluation and outcomes of patients with palpitations. The American Journal of Medicine. 1996. PMID: 8629647.
• Thuisarts. Ik heb last van hartkloppingen. thuisarts.nl.