The wall of the aneurysm is thin, as seen here in cross section, but it is formed of dense collagenous tissue, so it does not rupture. However, the aneurysm is formed of non-functional tissue that does not contract, so the ejection fraction and stroke volume of the heart are reduced. In addition, mural thrombus can form in the aneurysm, and is seen here as the dark red layers extending inward from the thin aneurysmal wall. Portions of the mural thrombus could break off and embolize to the systemic circulation.