Supraventricular tachycardia (SVT) is an abnormally fast heart rate of over 100 heartbeats a minute.
You'll usually feel your heart suddenly start racing and going very fast, then stop or slow down abruptly. You may also experience:
Episodes of SVT can last for seconds, minutes, hours or even days, in rare cases. They may occur several times a day, or only once or twice a year.
Read more about the symptoms of SVT.
When to seek medical help
SVT is rarely life-threatening, but you should contact your GP as soon as possible, if you experience symptoms.
A test called an electrocardiogram (ECG) can be used to confirm a diagnosis of SVT, if the heart is still racing. Occasionally, an ECG can show abnormalities that suggest you have SVT, even when your heart rhythm returns to normal.
As SVT can sometimes be difficult to diagnose, your GP may refer you to a cardiologist (heart specialist) who specialises in treating heart rhythm disorders, called an electrophysiologist.
Dial 999 to request an ambulance if you experience severe chest pain or breathing difficulties and you feel faint.
Read more about diagnosing SVT.
What causes SVT?
SVT occurs when there's a problem with the heart's electrical system, which controls your heart rhythm. This causes the heart to beat much faster than normal.
In some people, SVT results from an extra electrical connection in the heart present from birth (Wolff-Parkinson-White syndrome), but it can also occur in hearts that are otherwise normal.
SVT can occur in anyone at any age and often starts for the first time in children or young adults. Generally, the fast heart rate happens more frequently and lasts longer the older you get.
SVT can be triggered by the extra heartbeats (ectopic heartbeats) that most people experience, but some episodes are brought on by things like drinking large amounts of alcohol or caffeine, stress, or smoking lots of cigarettes.
Read more about the causes of SVT.
Most episodes of SVT are harmless, don't last long and settle on their own without treatment. However, the symptoms are often troublesome and treatments are available to stop ongoing episodes and prevent them occurring in the future.
Ongoing episodes of SVT can sometimes be stopped using certain manoeuvres, such as the Valsalva manoeuvre, that slow down the electrical impulses in the heart by stimulating a nerve called the vagus nerve. The Valsalva manoeuvre usually involves holding your nose, closing your mouth and trying to exhale hard, while straining as if you were on the toilet.
If manoeuvres like this are ineffective, injections of medication or an electric shock treatment called cardioversion can usually help to stop ongoing SVT episodes.
To prevent future episodes, medication that's taken every day can be prescribed. However, the definitive treatment is a procedure called catheter ablation, which involves destroying the tiny areas of the heart that are causing problems. It's very effective at preventing future episodes.
Read more about treating SVT.