Hypoplastic Right Heart Syndrome (HRHS) is a condition that is even more rare than Hypoplastic Left Heart Syndrome (HLHS). HRHS refers to the underdevelopment of the right side structures of the heart, which means that the chambers, valves and related blood vessels on the right side of the heart are malformed. This malformation involves the pulmonary valve atresia which has not formed, a very small right ventricle