Aneurysms are a result of a weakened blood vessel or heart chamber wall and may be a result of a hereditary condition or an acquired disease.

As an aneurysm increases in size, the risk of rupture increases, leading to uncontrolled bleeding. Although they may occur in any blood vessel, particularly lethal examples include aneurysms of the Circle of Willis in the brain, aortic aneurysms affecting the thoracic aorta, and abdominal aortic aneurysms which supply blood to the entire body.

Aneurysms can also arise in the heart itself following a heart attack.