WHY IS PECTUS EXACAVATUM OR CARINATUM
First, because such a chest does not look aesthetically acceptable. Either it is pectus carinatum (pigeon chest)...
or funnel chest or both...
Second, because there may exist serious medical issues behind a deformed chest
1. During childhood and adolescence even a severely deformed chest may not pose any major trouble due to its flexibility. This elasticity diminishes with age to become adult-type rigid around the age of 19 years. The increase in a deformed chest stiffness usually reduces its respiratory efficiency. It does so less in pectus carinatum than in pectus excavatum where it may often become very severe.
2. The depressed breastbone exerts pressure on the underlying heart and may affect its shape with resulting heart valve dysfunction.
3. The compressed heart moves left and reduces the left lung compartment.
4. How compression of the heart affects its coronary vessels needs further study.
5. A rigid, deformed chest significantly contributes to backbone deformities, kyphosis and scoliosis.