BRITAIN: Tony Blair's condition, Supraventricular tachycardia (SVT), is a relatively common but benign rhythm disturbance of the heart.
Supraventricular refers to the abnormal rhythm's origin in the area of the heart above the main chambers (the ventricles). Tachycardia is the medical name for a heartbeat greater than 100 beats per minute.
The symptoms of SVT include palpitations - typically a feeling that the heart is racing, or missing a beat and chest pain. Shortness of breath and dizziness may also occur and reflect the fact that the heart is not operating as efficiently as usual because of its chaotic beat.
SVT's are usually self-limiting even without treatment. They can last from seconds to hours. They do not signal underlying heart defect in the way that other rhythm disturbances can.
Medical treatment involves the use of medication in the form of a rhythm regulator or, as in the care of Mr Blair, the application of a mild electric shock to the chest wall to "kick-start" a normal rhythm. The technique of cardioversion involves the use of paddles placed on the chest in a procedure similar to the "shocking" of a patient who has collapsed following a heart attack.
An SVT may become recurrent, in which case preventive medication is usually prescribed.