Complex sentence: Supraventricular tachycardia (SVT) arises from improper electrical activity of the heart which presents as a rapid heart rhythm originating at or above the atrioventricular node.
Split into simpler sentences: Supraventricular tachycardia (SVT) is a cardiac arrhythmia arising from improper electrical activity of the heart. It is a type of tachycardia (rapid heart rhythm) originating at or above the atrioventricular node.