Atrial septal defects of 4mm have the potential to heal, mainly related to age. The atrial septum is located between the right and left atria, the septum slopes to the left anteriorly and is divided into muscle fibers and connective tissue. Atrial septal defects are one of the most common congenital heart defects in adults. Small secondary atrial septal defects have a 15% self-healing rate and most occur before the age of 4 years, especially within the first year of life. Therefore, the ability of atrial septal defects to heal spontaneously is closely related to the age of the child and the location and size of the defect. If it does not heal spontaneously, a 4mm atrial septal defect needs to be repaired in childhood, otherwise there is a potential risk of heart failure and pulmonary hypertension in adulthood. If you feel unwell, please seek medical attention.