This is the dilatation or ballooning of a section of the aorta which is the main artery coming out and away from the heart.  An aneurysm usually occurs because of an underlying weakness in the wall of the aorta at that point.

Very often you will not have any symptoms from the aneurysm and it may only be discovered through a chest x-ray or CT scan.  If the aneurysm begins to get larger or leak, you may experience chest or back pain.

If there is a risk of the aneurysm bursting, surgery will be required.