Although the veterinary term 'Pectus Excavatum' is sometimes used for FCK, that is inaccurate. Pectus excavatum refers to the sternum (breastbone) growing pointing inwards into the body: a few FCKs also have pectus excavatum, but many do not and a flat chest is not the same thing as an ingrowing sternum. I am very grateful to one of the breeders who read this page for sending this x-ray of pectus excavatum:

In FCK the underside of the ribcage flattens and sometimes caves in. I believe that the majority of cases of FCK go undiagnosed: when the condition is only mild the kitten does not show any signs of distress or weakening and can thrive as a normal kitten. The ribcage will right itself with time. A mild case of FCKS probably requires no intervention, although supplementing with vitamins and - if the kitten is one of a large litter - with additional milk, is highly advisable to prevent the condition from worsening.

Usually in extreme cases the kitten will start gasping for breath and will die if left. Sometimes the flattening does not cause breathing difficulties and the kitten can survive. Once the ribcage is pulled inwards though, there is a danger of lung damage, and some kittens who appear to do well at first nevertheless die, and autopsy has shown abnormal lung tissue. The two diagrams below were produced in a veterinary study that was commissioned by the Burmese Cat Club (details further on).

In terms of the flattened chest of a FCK, the muscles between the ribs (intercostal muscles) and the muscles of the diaphragm do not contract and relax correctly, so the whole volume of the chest cavity becomes smaller and the lungs are not properly inflated or deflated. Less oxygen is able to get to the muscles and the kitten tries to get the extra oxygen by breathing faster -- i.e. appears to be panting.

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