Definition. Tricuspid atresia is a heart defect present at birth (congenital) in which one of the valves (tricuspid valve) between two of the heart's chambers — the upper right chamber (right atrium) and the lower right chamber (right ventricle) — isn't formed.efinition. Tricuspid atresia is a heart defect present at birth (congenital) in which one of the valves (tricuspid valve) between two of the heart's chambers — the upper right chamber (right atrium) and the lower right chamber (right ventricle) — isn't formed.