Sudden Racing Heartbeat
Quick answer
A heartbeat that suddenly races and then stops may come from a rhythm problem such as SVT, or less often dangerous ventricular rhythms. Caffeine, anxiety and thyroid problems can also cause palpitations. A doctor should record an ECG. Fainting, chest pain or breathlessness with racing needs emergency care.
Medically reviewed by The Curaventa Team · Last updated 2026-10-24
Get urgent care if
- Fainting or near-fainting
- Chest pain
- Severe breathlessness
- Racing heart in someone with previous heart attack
Possible causes
| Condition | Why it can cause this |
|---|---|
| Supraventricular Tachycardia (SVT) | abrupt start and stop, often in younger people |
| Ventricular Tachycardia (VT) | more serious, often with known heart disease |
| Mitral Stenosis | can trigger atrial fibrillation |
| Overactive thyroid | causes fast pulse and weight loss |
| Anxiety or stimulants | caffeine, energy drinks or stress |
Tests a doctor may order
- ECG, ideally during symptoms
- Holter or event monitor
- Echocardiogram
- Thyroid blood test
Next steps
- Try to record an ECG or smartwatch tracing during an episode
- Note how it starts, stops and how long it lasts
- Reduce caffeine and energy drinks
- See a cardiologist for recurring episodes
Frequently asked questions
Can a smartwatch detect SVT?
Some can record a single-lead ECG. This may help doctors. It does not replace a full assessment.
Is a racing heart dangerous?
Many episodes are harmless, but some rhythms are serious. Warning signs include fainting and chest pain. A doctor should assess recurrent episodes.
Can I stop an episode myself?
Some people learn vagal manoeuvres from their doctor. Do not try them without guidance. Seek help if the episode does not stop.
Medically reviewed by The Curaventa Team. Last updated 2026-10-24. General information, not medical advice. Medical editorial board · Editorial policy · How we get prices
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