What is aortic knuckle?

Q: What is aortic knuckle? What happens if you can't notice it? Also, what happens if the right atrium is enlarged?

A:These are anatomical details which are of no use to the layman except in the context of some illness. The answers are as follows :1. It is the curvature of the aorta seen in an X-Ray film on the right side of the Cardiac Silhouette.2. Nothing3. Nothing unless the patient has a malformation involving some of the other heart chambers.