Diaphragm paralysis is a rare complication in pediatric heart surgery (0.28%-5.6%, depending on the procedure). When unilateral paralysis happens in adults, it is rarely symptomatic. However, it can cause respiratory distress syndrome when it happens in newborn or young children. The clinical diagnosis comes with a failure to wean from ventilation. The chest X-ray shows the ascension of the concerned hemidiaphragm. The goal of the surgical treatment is to pull down the paralyzed diaphragm and to increase the ventilating capacity. The classical surgical approach is a posterior-lateral thoracotomy in the 5th intercostal space of the concerned paralyzed hemidiaphragm. This approach has several drawbacks such as requiring drainage, reopening the chest after heart surgery, the high level of pain, and the cosmetic side effects. The subcostal approach is a good alternative because it is less time- consuming, it does not require any drainage, and it is less painful. This video-tutorial describes the abdominal approach and provides its advantages compared to a thoracotomy.