Tricuspid atresia is a heart defect present at birth (congenital) in which a valve (tricuspid valve) between two of the heart’s chambers isn’t formed. Instead, there’s solid tissue between the chambers, which restricts blood flow and causes the right lower heart chamber (ventricle) to be underdeveloped.
https://www.mayoclinic.org/diseases-conditions/tricuspid-atresia/symptoms-causes/syc-20368392

