Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Hypoplastic right heart syndrome ?
    ### Response:
    Hypoplastic right heart syndrome is a rare heart defect, present at birth (congenital), that results in low blood oxygen levels. It is caused by underdevelopment of the structures on the right side of the heart (tricuspid valve, right ventricle, pulmonary valve, and pulmonary artery) and commonly associated with atrial septal defect.
    