Atrial septal defect type 2 refers to a secondary foraminal septal defect, which is located in the fossa ovalis and is caused by either arrested development of the secondary septum or over-absorption of the primary septum. If the base of the foramen ovale is foramen ovale-type, multiple defects can be seen, and the size of the defects varies widely, ranging from less than 3 mm to more than 20 mm. Secondary foraminal septal defects can be associated with other types of atrial septal defects. Patients who are younger and have defects less than 7-8 mm in diameter may experience spontaneous closure or smaller defects, while patients with medium to large atrial septal defects are less likely to have spontaneous closure, and may become symptomatic before the age of 40. The diagnosis of secondary foraminal septal defects can be confirmed by chest wall echocardiography, and those who fail to have spontaneous closure need to be treated with surgery as soon as possible. The diagnosis can be confirmed by chest wall echocardiography.