The location of the specialized cardiac conduction system in patients with univentricular hearts may be extremely variable. Electrophysiologic studies during open heart surgery identified the intraventricular conducting tissue to be consistently located in four sites. In patients with univentricular hearts without an outlet chamber, conducting tissue may be located either at 1. along the posterior wall or 2. along the anterior free wall of the ventricle. In patients with univentricular hearts and an outlet chamber, conducting tissue is uusally located anterior and superior to the bulboventricular foramen and then extends towards the atrium either 1. in between the bulboventricular foramen and the pulmonary valve or 2. along the right margin of the pulmonary artery over the anterior free wall of the ventricle towards the junction of the inter-atrial septum and the right atrial appendage. These electrophysiologic studies are consistent with previously described locations of conducting tissue in similar hearts by histologic methods. The different locations of the intraventricular conducting tissues in patients with univentricular hearts demonstrates the valve and the need for electrophysiologic mapping of the specialized cardiac conduction system during surgical repair of univentricular hearts.