Whole hearts were removed from Hand2fl/fl [A] and Hand2flneo/flneo [B] E18.5 embryos and 20 μm frozen transverse sections were visualized following staining with Hematoxylin and Eosin. Misexpression of Hand2 [B] consistently results in enlarged hypoplastic right ventricles and disorganized trabeculations. Abbreviations: right ventricle (RV), left ventricle (LV), aorta (Ao). Scale bars indicate 100 μm [A,B] and 25 m [A1,A2,B1,B2].