Traditional views suggest that the best age to close atrial septal defects (ASDs) is between four and five years old, during preschool. The possibility of spontaneous closure of atrial septal defects larger than 8 millimeters in diameter is very low. If the defect is less than 4 millimeters, there is a possibility of healing. Currently, it is advocated that if an atrial septal defect still exists after the age of one year, and there is evident systolic murmur and fixed splitting of the second heart sound, or if heart catheterization and echocardiography show left-to-right shunting greater than 1.5:1, indicating a defect diameter of five to six millimeters or more, early surgery should be pursued to stop the left-to-right shunt to avoid causing pulmonary hypertension and endocarditis.