A-D: Representative of serially sectioned H-E stained images of wild-type (A), Tgfb1−/− (B), Tgfb2−/− (C) and Tgfb3−/− (D). Only Tgfb2−/− mice develop dysplastic or enlarged cushions (C, arrows) (see Results section for a quantification of total cushion cells). Notably, this mutant heart also has overriding tricuspid valves. Scale bar: 200 µm (A–D). TV, tricuspid valves; MV, mitral valves; RA, right atrium; RV, right ventricle; LV, left ventricle.