The heart has an electrical conduction system which carries the driving signals from the natural pacemaker of the heart situated in the upper right chamber to the lower chambers. Usual conduction is from the natural pacemaker known as SA node (sinoatrial node) to the AV node (atrioventricular node) and to the ventricles through a conduction bundle known as bundle of His. In some persons there are accessory conduction pathways which bypass the AV node. Such accessory conduction pathways are rare, but can cause abnormal rhythms of the heart with very fast heart beats, which can sometimes be irregular as well. Accessory pathways causing abnormal heart rhythms are often called WPW syndrome (short for Wolff–Parkinson–White syndrome).
When there is an accessory pathway in certain situations, the signals from the upper part of the heart can return through it back to the upper chambers of the heart causing a circus movement in some sort of a short circuit in the centre of the heart. This rapid cycling of electrical signals in the centre part of the heart causes rapid heart beats if part of it is conducted down to the lower chambers. This disorder can be treated by catheter ablation.