Wolff-Parkinson-White syndrome is a disorder of the electrical system of the heart. It is caused by the presence of an abnormal accessory electrical conduction pathway between the atria and the ventricles. Electrical signals travelling down this abnormal pathway (known as the bundle of Kent) may stimulate the ventricles to contract prematurely, causing a unique type of supraventricular tachycardia referred to as an atrioventricular reciprocating tachycardia. It affects 0.1-0.3% in the population. Sudden cardiac death in patients is rare (<0.6%), and is usually caused by the propagation of an atrial tachydysrhythmia (rapid and abnormal heart rate) to the ventricles by the accessory pathway.