The blue baby syndrome known as tetralogy of Fallot consists of an incomplete wall between the ventricles ( known as a ventricular septal defect or VSD ); an aorta that sits over this defect so that its blood comes from both ventricles instead of just from the left ( overriding aorta ); a defective right ventricular outflow tract near the pulmonary valve that prevents full flow of blood to the lungs; and a muscular right ventricle necessary to accomplish the extra work required to overcome that defect ( right ventricular hypertrophy ).
