Here is a severe form of endocardial cushion defect in which there is only a single large atrioventricular valve, as seen from above, that separates a single ventricle from a single atrium. This patient was able to survive with this two-chambered heart because a small amount of residual interventricular septum provided some direction to flow of oxygenated and unoxygenated blood, and also because of pulmonic stenosis, which protected the lungs from the shunting. (This is an explanted heart from a cardiac transplantation procedure, so most of the atria are not present.)