Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Cor triatriatum ?
    ### Response:
    Cor triatriatum is an extremely rare congenital (present at birth) heart defect. The human heart normally has four chambers, two ventricles and two atria. The two atria are normally separated from each other by a partition called the atrial septum and the two ventricles by the ventricle septum.
    