Our long-term follow-up has revealed that symmetrical development of the breasts is significantly impaired in pre-pubescent female patients subsequent to an anterolateral thoracotomy. Although standard posterolateral and anterolateral right-sided thoracotomies are used for correction of "simple" cardiac lesions such as patency of the arterial duct, coarctation of the aorta, or atrial septal defect, the required partial transection of large muscle groups, and injury to the developing tissues of the breast, may contribute to an unfavourable cosmetic outcome. Over the years, many surgeons, mostly specialising in thoracic procedures, have advocated mini- or axillary thoracotomies. In an attempt to improve surgical and cosmetic outcome, we have now adopted such a muscle-sparing approach, using a small horizontal midaxillary incision. We have now successfully employed the technique to close atrial septal defects in the oval fossa in 17 pre-pubescent females.