 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.Aneurysms can arise in the heart itself following a heart attack, including both ventricular and atrial septal aneurysms.There are congenital atrial septal aneurysms, a rare heart defect.