Types of Atrial Septal Defects

This drawing illustrates the location of the three general types of congenital atrial septal defects. The sinus venosus defect is the least common and it is found in the superior portion of the septum, near the entry of the superior vena cava. It is often associated with partial anomalus pulmonary venous drainage of the right superior pulmonary veins. An ostium secundum defect is the most common type of atrial septal defect. It lies in the mid portion of the septum, in the area of the fossa ovalis. The ostium primum defect is just superior to the atrioventricular valves. It is an endocardial cushion malformation and almost always is associated with a cleft anterior leaflet of the mitral valve.