Coloured 3D computed tomography (CT) angiogram scan of the chest of a patient with coarctation of the aorta, the body's main artery. This is a congenital (present at birth) defect, where part of the aorta is narrowed. This narrowing causes the heart to need to beat harder to pump blood around the body. In this case some blood flow has been restored by the development of smaller blood vessels that provide an alternate route around the narrowed aorta. This is known as collateral circulation. Mild cases of coarctation may not be diagnosed until adulthood, but severe cases can lead to heart failure and death if not treated.