3D coloured computed tomography (CT) scan of the heart of a patient with Kommerell diverticulum, a rare congenital (present from birth) anomaly of the aortic arch (upper centre). The aorta (down centre) is the main artery that carries blood from the heart to the rest of the body. A diverticulum is a bulging pouch, which can be seen here just below where the subclavian artery branches from the aortic arch. Kommerell diverticulum may be asymptomatic or cause symptoms due to the compression of surrounding structures such as the trachea (wind pipe) or oesophagus (gullet). A possible complication is rupture of the diverticulum, which can be fatal. Therefore, surgical intervention to repair or replace the aortic arch is necessary.