D-Transposition, also known as dextro-Transposition of the great arteries (d-TGA), is a congenital heart defect where the ventricles are connected to the wrong great arteries. Specifically, the aorta arises from the right ventricle while the pulmonary artery arises from the left ventricle. This causes two parallel circulations instead of the normal series circulation. The basic embryological defect is abnormal development of the conus, which prevents normal septal formation between the great arteries. Untreated d-TGA is fatal in infancy due to lack of oxygenated blood to the body. Clinical presentation depends on the degree of mixing between the circulations.