A rare type of atrial septal defect.

A previously unrecorded cardiac anomaly is described. A defect existed in the lowest part of the atrial septum straddling the orifice of the inferior vena cava so that this vessel opened into both atria. There was an associated anomalous connexion of the right pulmonary veins to the right atrium. The septal defect was recognized only at necropsy. As in the case of a sinus venosus atrial defect, it is suggested that the fundamental embryological error responsible for the production of the rare defect here described is laevo-position of the sino-atrial orifice.