Illustration showing aortic insufficiency, an inability of the aortic valve to close. Blood flows out of the aorta back into the left ventricle, placing an excessive burden on the left half of the heart. This is caused by endocarditis (inflammation of the heart's inner lining). After the inflammation has subsided, the leaflets of the flap may have shrunk so much that a closure is no longer possible and a triangular opening remains. If aortic valve insufficiency is left untreated, congestive heart failure will result. Aortic insufficiency can require the aortic valve to be replaced.