Hypothyroidism and palpitations: what to know

Palpitations can feel like pounding, racing, fluttering or skipped beats. An underactive thyroid itself more often slows body processes, while too much thyroid replacement or a change in thyroid function can make the heart feel fast. Palpitations may also occur with dehydration, anaemia, low blood sugar, anxiety, an irregular rhythm or another heart condition.

The pattern helps: note whether episodes begin suddenly, happen at rest or with activity, last briefly or continue, and whether the pulse feels regular. These details help distinguish a sensation from a rhythm problem, but they cannot diagnose the cause by themselves.

Sit down, breathe slowly and avoid driving if you feel faint. If you can, record the time, duration and pulse rate, plus caffeine, illness, missed meals or a recent medicine change. Take thyroid medicine exactly as prescribed and do not adjust the dose yourself. Drink fluids if you may be dehydrated and able to do so. Arrange a medical review for new, frequent or persistent episodes; an examination, blood tests or heart tracing may be needed.

Call emergency services for palpitations with chest pain, severe breathlessness, fainting, new confusion, or marked weakness. Urgent assessment is also appropriate if the heartbeat remains very fast or irregular, or if symptoms occur with swelling and difficulty breathing. Do not assume palpitations are caused by thyroid disease when these warning signs are present.

Ask whether your thyroid dose and recent thyroid tests need review, whether an electrocardiogram is suitable, and whether anaemia, dehydration, low blood sugar or an irregular rhythm could be contributing. Tell the clinician about all medicines, supplements, stimulants and episodes of dizziness.