Atrial septal defect accounts for about 20%-30% of all congenital heart diseases and is more common in females. Many cases are mild in children and are not discovered until adulthood. Atrial septal defects can be classified based on anatomical abnormalities into patent foramen ovale, primary atrial septal defect, and secondary atrial septal defect. A patent foramen ovale generally does not cause shunting between the two atria. A primary atrial septal defect is located at the lower part of the atrial septum, is semicircular in shape, and is often larger, frequently associated with malformation of the mitral or tricuspid valves resulting in regurgitation. A secondary atrial septal defect is situated in the middle of the atrial septum at the fossa ovalis or near the superior and inferior vena cava. The symptoms of an atrial septal defect vary with the size of the defect; minor cases may be asymptomatic, while severe cases can result in heart failure.