Browse A-ZABCDEFGHIJKLMNOPQRSTUVWXYZ0-9 Heart valves - superior view There are four valves located in the heart. Each valve either consists of two or three folds of thin tissue. When closed, the valve prevents blood from flowing backwards to its previous location. When open the valve allows blood to flow freely. Valve problems can occur because of congenital abnormalities, infection, or other causes. Review Date: 6/2/2014 Reviewed By: The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M. content is best viewed in IE9 or above, Firefox and Google Chrome browser.