Medically reviewed by Dr Nabila Laskar, Consultant Cardiologist (GMC 7040901). SVT is a fast heart rhythm arising above the ventricles, typically starting and stopping abruptly with rates of 140–250 beats per minute.
A sudden switch to a very fast, regular heartbeat, often described as a light switch turning on and off. Episodes may last minutes or hours and can cause breathlessness, chest discomfort, light-headedness and anxiety. See /conditions/heart-palpitations.
Caffeine, alcohol, stress, dehydration, lack of sleep, stimulant medication and hormonal changes. Many episodes occur with no identifiable trigger at all.
Capturing the rhythm is essential: a 12-lead ECG during an episode is diagnostic, and ambulatory Holter monitoring (see /conditions/holter-monitor) is used when episodes are intermittent. An echocardiogram confirms the heart is structurally normal.
Vagal manoeuvres taught by your doctor can terminate episodes. Medication may reduce frequency, and catheter ablation offers a high cure rate for most SVT circuits — usually the definitive option for frequent or disabling episodes.
In a structurally normal heart SVT is rarely life-threatening, although it can be very distressing and can cause fainting if the rate is extremely fast. It should still be formally diagnosed, because other fast rhythms need different management.
Catheter ablation cures the majority of common SVT circuits with a high long-term success rate, making it the preferred option for many people with frequent episodes. Whether it is right for you is decided with a cardiologist and electrophysiologist.
Vagal manoeuvres such as bearing down or the modified Valsalva often terminate an episode. Your cardiologist will show you the correct technique. If an episode does not stop, or you have chest pain or faint, seek emergency care.
No. SVT is a regular, organised fast rhythm, while atrial fibrillation is irregular and disorganised and carries a stroke risk requiring separate assessment. See /conditions/atrial-fibrillation.