An aortic aneurysm is a balloon-like bulge in the aorta, the large artery that carries blood from the heart through the chest and torso.

Aortic aneurysms can dissect or rupture:

The force of blood pumping can split the layers of the artery wall, allowing blood to leak in between them. This process is called a dissection.
The aneurysm can burst completely, causing bleeding inside the body. This is called a rupture.
Dissections and ruptures are the cause of most deaths from aortic aneurysms.