Paroxysmal supraventricular tachycardia(PSVT) is a very fast heart rate that begins and ends suddenly. PSVT occurs due to problems with the electrical connection between the atria and the ventricles. In PSVT, electrical signals that begin in the atria and travel to the ventricles can re-enter the atria, causing extra heartbeats. This tends to occur in young people or during vigorous exercise.
Attribution: Straight Talk Foundation