The tricuspid valve is normally made of three parts, called leaflets or flaps. The leaflets open to allow blood to move from the right atrium (top chamber) to the right ventricle (bottom chamber) while the heart relaxes. They close to prevent blood from moving from the right ventricle to the right atrium while the heart pumps.
In persons with Ebstein's anomaly, the leaflets are unusually deep in the right ventricle. The leaflets are often larger than normal. The defect usually causes the valve to work poorly, and blood may go the wrong way. Instead of flowing out to the lungs, the blood flows back into the right atrium. The backup of blood flow can lead to heart swelling and fluid buildup in the body. There may be narrowing of the valve that leads to the lungs (pulmonary valve).
In many cases, patients also have a hole in the wall separating the heart's two upper chambers and blood flow across this hole may cause oxygen-poor blood to go to the body. This can cause cyanosis, a blueish tint to the skin caused by oxygen-poor blood.
Ebstein's anomaly occurs as a baby develops in the womb. The exact cause is unknown, although the use of certain drugs (such as lithium or benzodiazepines) during pregnancy may play a role. The condition is rare. It is more common in white people.