The heart is split into four parts. Two collecting chambers at the top called Atria (Atrium) and two pumping chambers at the bottom called Ventricles. The ventricles are normally larger to allow them to pump with enough power. In Ebstein's anomaly the Tricuspid Valve which separates the Right Atrium from the Right Ventricle is fixed in the wrong position (too low) making the Right Ventricle much smaller an therefore less powerful than it should be. This means that the heart struggles to pump blood effectvely to the lungs. In addition to this the valve may leak blood backwards. The range of severity is wide and some people manage with little need for anything more than medication, others will require complex surgery.