The most common complication of atrial septal defect is pulmonary hypertension, which can be classified as mild, moderate, or severe. Generally, mild pulmonary hypertension is not a major issue and is not considered very serious. However, moderate to severe pulmonary hypertension often accompanies repeated coughing, shortness of breath after exercise, or difficulty breathing. This situation is relatively serious and it is advisable to undergo surgery as soon as possible. If the condition reaches a severe stage, pulmonary hypertension could continuously increase. Furthermore, in patients with severe pulmonary hypertension, closing the atrial septum can lead to severe breathing difficulties and increased shortness of breath. Therefore, it is crucial to closely monitor patients with pulmonary hypertension.