Supraventricular Tachycardia (SVT) is a heart rhythm disorder featuring episodes of abnormally fast heart rate lasting for seconds, minutes, hours or, in rare cases, days. Episodes may occur regularly or very infrequently (sometimes years apart).
The rate may be as high as 300 beats per minute, but is usually between 140 and 220. It is caused by abnormal, fast, electrical spontaneous impulses that arise in the atria, the upper chambers of the heart and override the natural pacemaker.
Attacks often come on for no obvious reason but may be triggered by exertion, emotional upset, coffee or alcohol.
In most cases, the heart is normal, although the symptoms may be uncomfortable.