Pectus excavatum.

The deformity of pectus excavatum is caused by a negative pressure in the anterior mediastinum sucking in the body of the sternum. This is usually due to the heart lying on the left side, leaving the mediastinum empty so that the sternum and costal cartilages are sucked in to fill the empty space. The operation consists of excising the deformed cartilages, mobilizing the sternum, and suturing the pericardial sac into a central position which corrects the deformity.