septal defects are the most common atrial septal defects. This defect can arise as a result of defects of the septum primum and the septum secundum. For the septum primum, the problem can arise as a result of excess resorption of the septum during the process of apoptosis in order to form the foramen secundum. For the septum secundum, its inadequate growth can cause atrial septal defect since it is supposed to grow and eventually overlap the foramen secundum so as to form the oval foramen. As the right atrial pressure is normally lower than the mean left atrial pressure, a persisting ostium secundum causes usually a left-to-right shunt (meaning that blood flows from the left to the right atrium, wherefore it is an azyanotic heart defect). Treatment Newborns with small foramen secundum atrial septal defects have been shown to spontaneously correct by the third or fourth year of life. Therefore, medical supervision is generally accepted as a preventive measure for those diagnosed in infancy, rather than surgical intervention or use of other medical devices. If surgery is required, it is performed using minimally invasive techniques via robotic surgery that often requires only a few days of hospital stay. Surgical intervention should result in full closure of the foramen secundum, and mortality rates are similar to those for general anesthesia. The repair can be made by suturing the atrial septum or, if the foramen secundum is large in size, a patch can be made from the patient's pericardium to fully separate each atrium. The synthetic material Dacron may also be used to create a repair patch. Inserting a catheter has proven to be a safe and successful method for closing the foramen secundum in children. This method avoids the symptoms that accompany most ostium secundum atrial septal defects. The catheter is inserted into the femoral vein in the leg and moved into place in the atrial septum. Transesophageal echocardiography is accepted as the method to monitor this procedure which, when performed correctly, has shorter recovery times than surgical intervention. Complications of catheter insertion often include nausea and vomiting, blood vessel obstruction, pain, and hemorrhage. The most common problem with this preventive measure is the incomplete closing of the foramen secundum. There is at present no drug therapy for foramen secundum atrial septal defects, although infective endocarditis is a postoperative concern. To prevent this condition, a prophylactic is used for six