organ part ascending aorta pars ascendens aortae ascending thoracic aorta The ascending aorta is the portion of the aorta in a two-pass circulatory system that lies between the heart and the arch of aorta[GO]. A portion of the aorta commencing at the upper part of the base of the left ventricle, on a level with the lower border of the third costal cartilage behind the left half of the sternum; it passes obliquely upward, forward, and to the right, in the direction of the heart's axis, as high as the upper border of the second right costal cartilage, describing a slight curve in its course, and being situated, about 6 cm behind the posterior surface of the sternum. The total length is about 5 cm in length [Wikipedia].