A potentially life-threatening cardiac valve disorder, characterized by the constriction or obstruction of blood vessels, in which a valve malfunctions so that blood is forced to flow backward rather than through the vessel. The condition may be present at birth or acquired as the result of an illness, such as rheumatic fever, syphilis, or bacterial endocarditis.

Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved.