Noun
the ascending part of the aorta as it emerges from the left ventricle
Source: WordNetDissection of the ascending aorta (type A) is a surgical emergency while dissection of the descending aorta (type B) can possibly be managed medically. Source: Internet
Dissection of the ascending aorta is an emergency because dissection may interrupt coronary blood flow and blood flow to the brain, neither of which tolerate ischemia particularly well. Source: Internet