Congenital heart defects in <i>Hes1</i> mutant mice.

<p>(A) E15.5 hearts in ventral wholemount views (left) and cryostat sections at the levels indicated showing a normal configuration of the ascending aorta (ao) and pulmonary trunk (pt) in <i>Hes1</i>^+/− hearts (top) and a dextraposed aorta overriding a ventricular septal defect (arrowhead) in <i>Hes1</i>^−/− hearts (middle (mild) and bottom (severe)). Note that the aorta in the bottom heart symmetrically overrides the ventricular septal defect. (B) Paraffin sections of E18.5 hearts in a frontal plane showing a ventricular septal defect (arrowhead) in a <i>Hes1</i>^−/− (middle and bottom) but not <i>Hes1</i>^+/+ heart (top). lv, left ventricle; rv, right ventricle. Scale bar: (A) 200 µm; (B) 500 µm.