Failure of the TRICUSPID VALVE in the HEART to close fully, thus permitting blood to leak back into the right atrium during contractions of the right ventricle. This reduces the heart's pumping efficiency, and right-sided heart failure usually results. Treatment for heart failure (using DIURETICS and ANGIOTENSIN-CONVERTING ENZYME (ACE) INHIBITORS) usually restores function, but sometimes heart surgery is required to repair or replace the defective valve.