Summary: to close the valve when the heart expands again. From R.D. Lockhart, G.F. Hamilton, and F.W. Fyfe, Anatomy of the Human Body, Lippincott 1959 (this was Bob's freshman anatomy textbook). This photograph, also from an autopsy specimen, shows the aortic valve from above, with a short segment of the aorta around it - about the same view as the anatomic illustration above it. The
Image Dimensions: 400 x 267
Image originally found here.