The use of the pulmonary autograft for aortic root replacement has renewed interest in the morphology of the arterial roots. In this article the basic construction of the roots, their anchorage, and their support from surrounding structures are reviewed. The arterial roots manifest a complex anatomy, with an intricate relation between the anulus and its adjacent structures, which span the transition from ventricle to the great vessel. The pulmonary root is anchored over its entire circumference to the thin myocardium of the free-standing pulmonary infundibulum. The anchorage of the aortic root is more extensive, being partly inserted into the thick left ventricular and septal myocardium and partly continuous with fibrous structures such as the membranous septum and the mitral valve. The pulmonary root is supported only by a slight collar of myocardium. The aortic root is better encased, supported by the more pronounced bulging of ventricular myocardium as well as the adjacent atrial myocardium and atrial septum. When the pulmonary autograft is used for aortic root replacement it will obtain maximum support from the surrounding tissues by implanting the autograft as proximal as possible. Copyright 1998 by W.B. Saunders Company