How large an atrial septal defect can heal spontaneously depends on the size of the defect and the shape of the defect. If the atrial defect is 3-4 mm in infants, it is usually self-healing if there is a crossover. If the atrial defect is larger than 5 mm, it is possible to be relatively small. The atrial defect may be small, 5-6 mm, when it is small, but with age, the defect may increase, and in this case it will not grow, so whether it can grow or not depends not only on the atrial defect, but also on the ultrasound image to see whether it has crossover and overlap to determine whether it can heal by itself.