SVT is usually caused by an abnormality in your heart's conduction system. In SVT, electrical signals get caught in a loop that goes round and round. The looping signals make the heart beat regularly but very quickly, about 160 to 220 times per minute. In SVT the looping signals are above the ventricles. In ventricular tachycardia Ventricular Tachycardia , the abnormal rhythm is caused by a problem in your ventricles.