Flat Chested Kitten (FCK)

Flat Chested Kitten Syndrome is a deformity of a kitten's ribs and sternum (breastbone). The medical term for this is Pectus Excavatum and it is also known as Funnel Chest. The term 'Swimmer Kitten' is sometimes used when a kitten with FCK crawls with both front legs out to the side of the chest in a paddling motion.

What are the symptoms?

The kitten's chest is flat, rather than rounded and the ribs bow out more than normal, along the kitten's sides. The sternum may also collapse inwards as the kitten breathes. In more severe cases, the sternum is permanently curved inward, creating a furrow along the kitten's chest.

As well as the flat or furrowed chest, the kitten may:

  • Pant or show open-mouthed, heavy breathing
  • Tire easily
  • Show a reduced activity level (lethargy)
  • Have a significant delay in growth
  • Have a general loss of condition
  • Have splayed front legs

The flat chest means that the kitten cannot expand his lungs properly with each breath. The muscles between the ribs and the muscles of the diaphragm do not contract and relax properly, so the kitten must make an effort to get enough oxygen to his body.

It will often look as if the kitten has a problem with his airways, such as a blockage or infection but on closer examination, the cause is found to be FCK. A heart murmur sometimes accompanies FCK as the heart is also affected by the lack of space within the chest.

What causes it?

It is not really known why some kittens develop FCK and others, even in the same litter, don't. There are several suggestions on why FCK occurs:

  • Environment - It may be caused by the surface the kittens are on being too flat, or hard or slippery. Also, perhaps the FCK was caused by bacteria or a virus.
  • Nutrition - It may be due to a taurine or calcium deficiency in the mother-cat during her pregnancy, causing the kitten's bones to be softer than usual.
  • Genetics - It may be a hereditary trait where the kitten inherited FCK from one or both of his parents. They may not have FCK themselves but may be carriers of the genes that cause the condition.

These are just some of the theories on what causes FCK. Experts such as vets, professionals, and breeders still don't know exactly what causes it.


The prognosis for these kittens is often uncertain. If the FCK is mild, the kitten may grow out of it without intervention and eventually have a normal, rounded chest. Twice daily physiotherapy, where the kitten's legs are gently flexed and massaged into the normal position, may help. This loosens and lengthens the muscles and tendons in the legs, allowing them to gradually develop into the correct position.

If a kitten has splayed legs and prefers to lie on his back or flat on his stomach, turning him to lie on his side and gently holding him that way for a few minutes, several times a day, often helps.

The kitten may need supplemental feeding with a kitten formula such as KMR or Just Born. This is to help maintain his weight and good condition, like kittens with FCK sometimes have trouble nursing from the mother cat. When the kitten is old enough, encourage him to walk, as this helps the chest return to a more normal shape.

Another treatment for FCK is surgical correction, which has proven to be successful. The most common surgical method used, is to fix the ribs and sternum to an external splint which moves them into the correct position. The earliest a kitten can have this surgery is at 8 weeks old.

If you suspect a kitten has FCK, it is best to take him to a vet for a full evaluation. In cases where the FCK is severe, the kitten may have to be euthanized if he is suffering or there is no hope for his recovery.

Mild FCK

If the FCK is mild or moderate, the kitten may grow up to be a normal, healthy cat.

This is Vegemite, who was born with moderate FCK, as well as a heart murmur. She has grown up into a happy and perfectly healthy cat.

Written by Tania Waterhouse

Tania Waterhouse lives in Perth, Western Australia. She specializes in rescuing orphaned kittens.

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One comment on “Flat Chested Kitten (FCK)

mani October 30, 2013
My boy has pectus excavatum and a deformed spine. He was the only one of the litter who survived and his prognosis wasn't good.  There was a school of thought that suggested keeping him really quiet, but he was a lively little guy while he had the breath to be, so I encouraged him to reach and climb and be as active as possible to encourage physical development (he was 10 weeks old when I got him).  I also massaged the ribcage and encouraged backward bending with his front legs stretched up over his head.  He seemed to love viewing the world upside down when I walked around with him in this extended position! Excellent nutrition also helped. The PE has definitely reduced as he does not become anywhere near as breathless.  He's now 18 months old and is compromised with the condition and a deformed spine, but has an excellent quality of life nonetheless.    I believe that vets consider flat chest and pectus excavatum to be two different conditions (as can be seen from the diagram, above).

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