a congenital defect in the septum between the atria of the heart, due to failure of the foramen primum or secundum to close normally; may involve atrioventricular canal cushions; occasionally there is strong evidence of autosomal dominant inheritance [MIM*108800]. In varying degree, it is also a common feature of the autosomal recessive Ellis-van Creveld syndrome [MIM*225500] and the autosomal dominant Holt-Oram syndrome [MIM*142900].