Heart rhythm causes
| Cause | What it typically feels like |
|---|---|
| Ectopic (extra) beats | A thud, skip or pause, often at rest or in the evening |
| Atrial fibrillation (AF) | An irregular, often fast heartbeat, sometimes with breathlessness or tiredness |
| Atrial flutter | A fast, regular heartbeat, often around 150 beats per minute |
| SVT (including AVRT and AVNRT) | A sudden, very fast, regular heartbeat that starts and stops abruptly |
| Ventricular tachycardia (rare) | A fast heartbeat, often with dizziness or fainting, usually in people with existing heart disease. This needs urgent assessment. |
Everyday triggers
- Caffeine in coffee, tea, cola and energy drinks
- Alcohol, especially binge drinking (sometimes called "holiday heart")
- Nicotine from smoking or vaping
- Stress, anxiety and panic attacks
- Lack of sleep and tiredness
- Strenuous exercise, or being dehydrated
- Recreational drugs, such as cocaine, amphetamines and cannabis
Medical causes
- An overactive thyroid (hyperthyroidism), or too high a dose of thyroid medicine
- Anaemia (a low blood count)
- Fever or infection
- Low blood sugar
- Low potassium or magnesium, for example after vomiting, diarrhoea or with some water tablets
- Pregnancy and the menopause, because of hormonal changes
- Some medicines, including asthma inhalers (salbutamol), decongestants, some antidepressants and some weight-loss products
- Other heart conditions, such as heart valve disease, heart muscle disease or previous heart attack
Often there is more than one factor: for example, a few harmless ectopic beats that become much more noticeable with stress, poor sleep and extra coffee. Small changes can make a big difference. See self-help and lifestyle.
This page gives general information and is not a substitute for personal medical advice. Last updated October 2026.