<unk> s refer to a group of congenital heart diseases that involve the inter-atrial septum.  The inter-atrial septum is the tissue that separates the right and left<unk> from each other. This tissue prevents arterial and venous blood from mixing with each other. If there is a defect in this septum, a direct communication between the<unk> can occur, which allows shunting, resulting in mixing of arterial and venous blood. It is possible for blood to travel from the left side of the heart to the right side of the heart, or vice versa. Shunting can result in cyanosis. The excess flow to the right atrium and the right ventricle causes enlargement of these organs, and the increased flow through the pulmonary artery eventually causes pulmonary hypertension.
Atrial septal defect
Atrioventricular canal defect
Atrioventricular septal defect
Ventricular septal defect
Tricuspid atresia
Persistent truncus arteriosus
Patent ductus arteriosus 
Patent ductus arteriosus