ABSTRACT
Normally the atria become electrically isolated from the ventricles during fetal development, apart from the AV junction (i.e. AV node plus bundle of His). Incomplete separation leads to an accessory AV pathway. The pathway may be situated anywhere across the groove between atria and ventricles. The most common site is the left free wall of the heart. Other locations are postero-septal, right free wall and rarely antero-septal. In a minority of patients there is more than one accessory pathway.
