either of two crescent-shaped heart valves, one, a pulmonary valve, at the junction
of the right ventricle
and pulmonary artery, the other, an aortic valve, at the junction of the left
ventricle and aorta, which keep
blood from flowing back
into the ventricles
Webster’s New World College Dictionary, 4th Edition. Copyright © 2010 by
Houghton Mifflin Harcourt. All rights reserved.