Aneurysms of the aorta are at times evaluated and treated by physicians from a number of specialties. Indeed, whereas cardiac surgeons operate on the ascending aorta and arch and vascular surgeons manage abdominal aortic aneurysms, at present the responsibility often falls to cardiologists to oversee the medical care of patients with aortic disease of all types. However, although formally trained in “cardiovascular medicine,” most cardiologists devote their attention to the heart and its coronary arteries, and relatively few have experience in the management of diseases of the aorta. It is therefore important that cardiologists acquire a sufficient knowledge base so that they can confidently evaluate and manage patients with aortic disease and know when it is appropriate to refer them for surgery. Toward this end, the purpose of this review is to summarize the current understanding of thoracic and abdominal aortic aneurysms. Thoracic aneurysms may involve one or more aortic segments (aortic root, ascending aorta, arch, or descending aorta) and are classified accordingly (Figure 1). Sixty percent of thoracic aortic aneurysms involve the aortic root and/or ascending aorta, 40% involve the descending aorta, 10% involve the arch, and 10% involve the thoracoabdominal aorta (with some involving >1 segment). The etiology, natural history, and treatment of thoracic aneurysms differ for each of these segments. Figure 1. Anatomy of thoracic and proximal abdominal aorta. (©Massachusetts General Hospital Thoracic Aortic Center. Used with permission.) ### Etiology and Pathogenesis Aneurysms of the ascending thoracic aorta most often result from cystic medial degeneration, which appears histologically as smooth muscle cell dropout and elastic fiber degeneration. Medial degeneration leads to weakening of the aortic wall, which in turn results in aortic dilatation and aneurysm formation. When such aneurysms involve the aortic root, the anatomy is often referred to as annuloaortic ectasia. Cystic medial degeneration occurs normally to some extent with …