Andersen–Tawil syndrome affects the heart by prolonging the QT interval, a measure of how long it takes the heart to relax after each heart beat. This, as in other forms of long QT syndrome, can lead to abnormal heart rhythms such as ventricular ectopy or ventricular tachycardia causing palpitations. The ventricular tachycardia seen in Andersen–Tawil syndrome often takes a form known as bidirectional ventricular tachycardia. The arrhythmias seen in association with the condition can cause sudden cardiac death, but the risk of this is lower than in other forms of long QT syndrome.