Ebstein anomaly is an abnormality in the tricuspid valve. The tricuspid valve separates the right atrium (the chamber that receives blood from the body) from the right ventricle (the chamber that pumps blood to the lungs).

In Ebstein anomaly, two leaflets of the tricuspid valve are displaced downward into the pumping chamber. The third leaflet is elongated and may be tethered to the wall of the chamber. Rarely, the valve is so deformed that it will not allow blood to flow easily forward in the normal direction (right atrium to right ventricle).

More commonly, these abnormalities cause the tricuspid valve to leak blood backwards into the right atrium when the right ventricle contracts (squeezes). As a result, the right atrium becomes enlarged. If the tricuspid regurgitation (leak) is severe enough, congestive heart failure can result.

If there is excessive backflow into the right atrium, the pressure within the right atrium becomes very high. Normally, a fetus has a communication, or hole, between the right and left atrium known as the foramen ovale or PFO. The PFO usually closes after birth.

In Ebstein anomaly, the high pressure in the right atrium keeps the PFO open. This connection allows unoxygenated ("blue") blood to flow from the right atrium to the left atrium, bypassing the lungs and going directly to the body. This will result in lower oxygen levels in the blood. This is why children with Ebstein anomaly may be blue or "cyanotic," and have low oxygen saturations.

Ebstein anomaly may occur with other heart lesions, such as pulmonary valve stenosis or atresia, atrial septal defect or ventricular septal defect. In addition, many patients with Ebstein anomaly have an accessory (extra) electrical conduction pathway in the heart potentially leading to episodes of abnormal fast heart rate called supraventricular tachycardia (this condition is known as Wolff-Parkinson-White syndrome).