The expression of Hey2 in the endocardial cells of the AVC and OFT and mesenchymal cells derived from those endocardial cells might explain the atrioventricular valve defects, pulmonary stenosis, tetralogy of Fallot, and tricuspid atresia found in the Hey2 knockout mice7,8. The gene discussed is HEY2; the disease is Tetralogy of Fallot.