Small atrial septal defects are <6 mm in diameter, medium sized defects are 6-8 mm in diameter, and large septal defects are >8 mm in diameter. 12 mm is a large septal defect with little chance of natural closure, and the larger the septal defect, the more severe the hemodynamic changes in the heart, which can have a serious impact on the child’s development and growth. The larger the septal defect, the more severe the hemodynamic changes in the heart, which can have a serious impact on the child’s development. At the same time, it is difficult to operate if the defect is large, and the risk of surgery is also high, so early detection and early treatment are necessary.