High Quality Content by WIKIPEDIA articles! Flat-chested kitten syndrome (FCKS), is a disorder in cats, wherein kittens develop a compression of the thorax (chest/ribcage) caused by lung collapse. In mild cases, the underside of the chest becomes flattened (hence the name of the condition); in extreme cases the entire thorax is flattened, looking as if the kitten has been stepped on. The kitten will appear to go from normal to flat in the space of about 2-3 hours, and will usually then stabilise.