A two-port atrial septal defect is an atrial septal defect in which both primary and secondary foramina are present, and is the most common type of atrial septal defect in clinical practice. The second foramen defect is most commonly located in the middle oval fossa of the atrial septum or near the superior and inferior vena cava. Because of the small pressure difference and fractional flow between the atria, early atrial septal defects that are not associated with other precordial disease usually have no obvious clinical symptoms. Most children are detected and diagnosed during a physical examination or when a murmur is heard during a cold or pneumonia. The condition is generally less severe than that of ventricular septal defects. If the disease is not detected until adulthood, it is often more severe due to higher pulmonary artery pressures and requires long-term treatment before being evaluated for surgical indications. Therefore, atrial septal defects require early surgical treatment.