The atrial septal defect of 33 mm is more serious, and this defect is larger, because the large left-to-right shunt will affect the blood volume of the body circulation and also increase the blood volume of the pulmonary circulation, which will lead to the growth retardation of the child and may induce heart failure later. In this case, the child will need to be treated with blockage after stabilization. If the atrial septal defect is large, we should pay attention to whether the child usually has cyanosis, easy to catch cold and lung infection.