Persistent truncus arteriosus is a congenital heart defect associated with a high mortality rate. In normal fetal development the truncus arteriosus divides into the aorta and pulmonary artery. If the truncus arteriosus persists beyond the fetal stage, a single arterial trunk arises from the normally formed ventricles, and blood from both ventricles will mix, affecting the pulmonary and systemic circulation. If the infant survives, pulmonary vascular obstructive disease often develops due to extreme hypertension (high blood pressure) in the lungs. This disorder is also often associated with ventricular septal defects. Persistent truncus arteriosus is also known as Buchanan syndrome, and approximately 35% of infants with persistent truncus arteriosus also have DiGeorge syndrome.