Obstruction to the left ventricular outflow tract is not uncommon in patients with congenitally corrected transposition. A case of congenitally corrected transposition is described with significant subpulmonary obstruction which was due to a subpulmonary tag. The patient required an aortopulmonary shunt. Her clinical course was subsequently significantly influenced by arrhythmias associated with an accessory pathway. She died suddenly from an arrhythmia. Post-mortem examination confirmed a large subpulmonary tag which originated from both sides of the ventricular septum—a previously unreported finding. Careful evaluation of the nature of left ventricular outflow obstruction is important in this condition as it may alter the surgical management.