Transposition of the great arteries is a form of congenital heart disease in which the aorta and pulmonary artery are transposed and arise from the incorrect ventricle. Instead of their usual origins (pulmonary artery arising from the right ventricle and aorta arising from the left ventricle) the great vessels arise abnormally (aorta arising from the right ventricle and pulmonary artery from the left ventricle). This is commonly referred to as ventriculo-arterial discordance. This lesion results in parrallel systemic and pulmonary circulations where deoxygenated blood is pumped out the aorta via the right ventricle and oxygenated blood re-circulates to the lungs via the left ventricle. A source of intracardiac mixing is required (i.e.- ASD, VSD or PDA) to avoid excessive cyanosis and death. The best site for mixing remains the atrial septum, but these patients commonly can also have VSDs or a persistent PDA following birth.