This defect is a downward displacement of the tricuspid valve (located between the heart's upper and lower chambers on the right side) into the heart's right bottom chamber (or right ventricle). It's usually associated with an atrial septal defect. While there is free flow of blood forward across the tricuspid valve to the right ventricle, the deformed tricuspid valve allows a large amount of blood to flow backwards from the right ventricle to right atrium when the right ventricle contracts. About 10% of cases are associated with chronic maternal lithium use. The treatment of this disorder depends on whether or not the person with it has any symptoms. Surgery is sometimes required early in life. On the other hand, people may have a normal life expectancy. Irregular and fast heartbeats (arrhythmia) frequently accompany this condition.