The aorta and the pulmonary artery are reversed; that is, the aorta rises from the right instead of the left ventricle, and the pulmonary artery arises from the left instead of the right ventricle. Systemic venous blood (unoxygenated blood) returns to the right side of the heart to pass through the aorta back to the body without being oxygenated because of bypassing the lungs. The pulmonary venous blood (oxygenated blood) enters the left side of the heart, returning to the lungs via the pulmonary artery. The systemic (unoxygenated) and pulmonary (oxygenated) circulations are totally separate. There must be some opening (i.e., patent ductus arteriosus or septal defect) to allow blood to mix. (From Ashwill, JW & James, SR: Nursing Care of Children: Principles and Practice. WB Saunders, Philadelphia, 2007.)