Aortic aneurysm. Coloured X-ray (angiogram) of an aneurysm (red swelling, lower centre) in the aorta of a 65-year-old man. His two kidneys (red) are at centre left and right, supplied by branching blood vessels (black). The aorta (black, running down from top centre) is the main body artery that runs from the heart down to the abdomen. An aneurysm arises from blood pressure stretching a weakened artery wall. This may be due to disease or an inherent weakness. A burst aneurysm will cause severe internal bleeding. Surgical replacement of the weakened section of the artery wall with a graft is usually required.