Ebstein's malformation, also called Ebstein's anomaly, is a congenital heart defect in which the tricuspid valve is abnormally formed. The tricuspid valve is one of the heart's four valves. It normally swings open to allow the smooth passage of blood from the right atrium to the right ventricle, and then closes. Blood should flow in one direction and only at the right time. The tricuspid valve normally has three "flaps," or leaflets. In Ebstein's malformation, one or two flaps are stuck to the wall of the heart and don't move normally. Ebstein's malformation is mild in most adults who have it, but sometimes the tricuspid valve leaks severely enough to result in heart failure or cyanosis. Then surgery may be required.