Fig. 5. Abnormal cardiac morphogenesis in E9.0 embryos with compound mutations in Hand1 and Hand2. (A-L) E9.0 embryos stained for lacZ activity expressed from the Hand1^lacZ allele. Left lateral view (A-F); frontal view of the heart (G-L). a, atrium; lv, left ventricle; rv, right ventricle; v, ventricular chamber. The asterisk in F shows the thin outflow tract present in the Hand1 cardiac-KO/KO; Hand2 KO/KO embryos. (M-X) Nuclear Fast Red counterstained transverse sections of embryos in A-L at anterior (M-R) and middle (S-X) levels of the heart. Genotypes of embryos are shown above each set of panels. Cardiac abnormalities increase in severity from left to right panels.