Cardiac defects in Cert^gt/gt embryos. (A) Images of E10.5 Cert^+/+ (+/+) and Cert^gt/gt (−/−) embryos. The heads were removed to facilitate the observation of the heart. In general, the mutant hearts were proportionately (relative to the size of the embryo) larger and thinner in the mutant compared with the wild type. (B, top) The same embryos in A were photographed from the other side to get a view of the left ventricle (LV), which, in this instance, appeared to have an area of increased density in the mutant embryo. The left bottom panel shows a mutant heart with accumulated blood in the left ventricle, and the panel on the right highlights the thin walls of the outflow tract (oft) and the left ventricle in the Cert^gt/gt hearts. (C) H&E sections of the wild-type (+/+) and mutant (−/−) heart show the proportionately larger heart of the mutant with thin-walled ventricles and the outflow tracts. The inset shows a high magnification view of the outflow tract. In this instance, the mutant outflow tract is larger, thin walled, and increased the amount of the acellular cardiac jelly seen inside the cavity.