A congenital diaphragmatic hernia, one of the more common malformations in the newborn (1/2000), is most frequently caused by failure of one or both of the pleuroperitoneal membranes to close the pericardioperitoneal canals. In that case the peritoneal and pleural cavities are continuous with one another along the posterior body wall. This hernia allows abdominal viscera to enter the pleural cavity. In 85% to 90% of cases the hernia is on the left side, and intestinal loops, stomach, spleen, and part of the liver may enter the thoracic cavity. The abdominal viscera in the chest push the heart anteriorly and compress the lungs, which are commonly hypoplastic. A large defect is associatd with a high rate of mortality (75%) from pulmonary hypoplasia and dysfunction.