A three-dimensional electroanatomic bipolar voltage map of the right atrium was performed in a 20-year-old patient with functional single-ventricle physiology after a classic Fontan-type operation who presented with clinical signs of heart failure, a dilated right atrium, protein-losing enteropathy, and sinus node dysfunction. Previous pacemaker upgrading to a DDD system using a transvenous right atrial lead had failed due to insufficient sensing and pacing function. The voltage map showed large zones of scarring and low-amplitude signals. Consecutively, conversion to an extracardiac total cavopulmonary connection (TCPC) together with a pacing lead insertion into the left atrium was performed successfully.