Heart racing for hours: what should you know?

A sustained fast pulse may follow dehydration, fever, pain, anxiety, low blood sugar, anaemia, or a medicine or stimulant. A persistent uneven rhythm can occur with atrial fibrillation or another heart rhythm disturbance.

Hyperthyroidism may cause ongoing fast beats with shaking, sweating, heat intolerance, or unexplained weight change. Heart failure can cause breathlessness, swelling, and tiredness. These associated features help a clinician decide which checks are needed, but they cannot diagnose the cause alone.

Stop activity, sit or lie safely, and ask someone to stay nearby if you feel unwell. Avoid caffeine, nicotine, alcohol, recreational drugs, and strenuous exertion. Sip water if appropriate, but do not force fluids or take unprescribed medicine.

Note when the episode started, whether the beat is steady or uneven, and any chest symptoms, breathing changes, fever, vomiting, or recent medicine changes. Contact a medical service promptly rather than waiting for repeated episodes.

Call emergency services now for chest pain or pressure, severe breathlessness, fainting, new confusion, one-sided weakness, or a persistent racing heartbeat with marked dizziness. Do not drive yourself if symptoms are severe.

Even without those warning signs, a racing heartbeat that continues for hours warrants same-day clinical assessment. The clinician may check your pulse and blood pressure, perform an electrocardiogram, and order blood tests.

Ask whether you need rhythm monitoring, blood tests for anaemia or thyroid problems, a medicine review, and clear instructions for the next prolonged episode.