Flat Chested Kitten Syndome
Part One: An Introduction

Adaped from an article by Julia Craig-McFeely

Published April 2006

Photos copyrighted by the individual photographers
Article copyright © ShowCatsOnline.com. All Rights Reserved.
Copying or redistribution of this article is strictly prohibited
without the express written permission of ShowCatsOnline.com

In this article we will discuss the condition called Flat Chested Kitten, along with its causes and prognosis. In Flat Chested Kitten Syndrome, Part Two, we will discuss various methods of treatment for the condition, especially splinting.


Kittens (and puppies) can suffer from several different chest wall abnormalities. In cats, the two most common are Pectus Excavatum ("funnel chest") and Flat Chested Kitten(FCK). It is important to understand the difference between the two conditions.

Pectus Excavatum

Pectus excavatum refers to the sternum (breastbone) growing pointing inwards into the body. Some flat chested kittens will also have pectus excavatum, but most do not. A flat chest is not the same thing as an ingrown sternum. Read the article titled Pectus Excavatum for more information on the condition.

The Flat Chested Kitten

FCK is an anonym for Flat Chested Kitten. In FCK, the underside of the ribcage flattens and sometimes caves in. In extreme cases, the kitten will start gasping for breath and will die if not aided.

Sometimes the flattening does not cause breathing difficulties and the kitten can survive without intervention. Once the ribcage is pulled inwards though, there is a danger of lung damage, and some kittens who appear to do well at first, but nevertheless die, and autopsy has shown abnormal lung tissue.

The Normal Thorax

The diagram on the right shows a side view and a cross section of a kitten's body showing the ribs and sternum bones and how they look in a normal kitten

Pectus Excavatum

Pectus excavatum is an unusual deformity of the breast bone, and refers to the sternum (breastbone) growing pointing inwards into the body. It can result in compression of the heart and lungs



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 unable to be 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 - and often appears to be panting.

There is another condition (unrelated to FCK) in which the sternum protrudes or sticks out, and though this apparently has no health implications, it is considered an anatomical fault.

Symptoms of FCK

Things to watch for include:

  • Flattening of the front of the chest
  • Often accompanied by a dip just behind the shoulder blades
  • Failure to Thrive
  • Difficulty in Breathing
  • Open mouth Breathing
  • Panting
  • Front legs splayed out to the sides
  • Protruding Elbows
  • Lethargic
  • Smaller Than Littermates

If You Suspect FCK

If you observe very carefully, you may actually see the rib-cage flattening. This usually happens between 2-10 days from birth.

Feel the 'walls of the chest' with your fingers and see if you can detect the flattening by finding a ridge running longwise at the sides of the ribcage.

It's very difficult to explain what a flat chest feels like in words, but if you can get hold of a reasonably fresh banana (yes, a banana) you can feel what a flattened ribcage is like.

Devon Rex kitten with FCK - note also the dip in the spine just below the shoulders (a survivor)

Egyptian Mau with FCK - note splayed elbows pushed out by the sides of the ribcage (another survivor)

"Feeling" for FCK

I've cut a banana in half so that you can see the shape in cross-section. Hold the banana with the flattest side downwards (usually on the inside of the curve). Hold it as illustrated, and draw your hand upwards. You can see that the outside of the skin has two clear ridges at the lower edge, and the bottom is flatter than the sides and top. This is almost exactly what a mildly flatten chest feels like (even down to the size) on a kitten - only with a covering of fur.

You may feel a slight ridge running along the ribcage in some kittens that does not progress into FCK, so don't panic!

What Happens in an FCK Kitten?

Normally the flat chest is simply that - flat. If, however, the muscles of the diaphragm are severely affected, they will pull the sternum into an abnormal position. The sternum will be pulled into the chest cavity, and this in turn will distort the shape of the heart and prevent the lung tissue from developing normally. This "pulling" action in FCK is sometimes confused with the condition called pectus excavatum. Unlike with pectus Excavatum, the sternum does not grow inwards in FCK.

The Degree of FCK

The severity of flat-chestedness varies greatly, even within a litter of affected kittens. Many slightly flat-chested kittens probably go unnoticed and grow out of it in time.

What Causes FKC?

There has been no long-term or serious study to determine the cause of FCK.

Generally, several theories of possible causes include:

  • Nutritional Factors
  • Environmental Factors
  • Genetic Factors

Indeed, having the condition manifest in a litter of kittens may rely on combinations of nutritional, environmental and genetic factors.


Various nutritional causes have been put forward for this condition developing. The Burmese Cat Club funded research into Taurine deficiency which, though it only had a very small study group to work with, concluded that it was not relevant.

Other theories suggested Potassium deficiency was the cause, but treatment with potassium supplements did not show significant results in treating the condition, and blood samples have not suggested a deficiency.

Environmental Factors

It has been hypothesized that any adverse event or stress during pregnancy, including poor nutrition, infections or antibiotics, may render a queen more liable to produce FCKs while a less stressful environment may prevent the condition from developing.

Perhaps the FCK was caused by bacteria or a virus.

There have even been some implausible theories for the cause for FCK - such as queens lying on heat pads or heated floors during pregnancy! This is simply not true.

Is FCK Genetic?

Some lines appear to throw FCK more than others.

It seems that there are numerous genetic markers that must be present in order for the condition to arise: if a cat has many of these markers then most of the offspring will have flat chests. If mated to another cat with a high level of markers, then all kittens in a litter will be flat. Single flat kittens may suggest that one of the parents carries a significant number of markers that were mitigated by the other parent being relatively free of them OR that there is an environmental rather than a genetic reason for the condition developing.

FCK does, however, also appears without any apparent genetic component.

If you have just one flat-chested kitten in a litter then the causes could be environmental more than genetic. It is rare to have a whole litter of flat chests unless both parents are strong carriers of the genetic cause, so it would be advisable to abandon a breeding line that produced whole FCK litters.

Which Breeds Get FCK?

All breeds of cat can produce kittens with FCK, including domestic and feral mixed breeds. Some breeds, particularly those with very limited gene pools, seem to be more prone to it.


The prognosis for FCK kittens depends upon the severity of their condition.

Mildly affected kittens often outgrow the condition.

If the kitten survives the initial onset of the condition, the prognosis is hopeful. Breeders also report kittens apparently doing well from 10-21 days of age who suddenly fade and die.

If the kitten survives beyond 3 weeks, then their chances of survival increases. The ribcage may revert to a normal shape if the condition is not too pronounced, or it may remain flat chested into adulthood with no apparent side-effects.

Kittens who are particularly small often have a compromised heart and may die at 12-18 weeks, or later. If the kitten is a normal size by 16 weeks and seems normal in every way, then it will probably is fine.

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.

Life Span

A kitten who has FCK that has resolved has every expectation of a normal life, as long as the compression has not affected the development of the heart or lungs. If a kitten runs and plays normally without getting out of breath or tiring quickly then it will probably be fine. Your vet should perform x-rays to assess the kitten more specifically.

Treatment Options

Mildly affected kittens may resolve without any intervention. There are however some treatments that you can try to increase your FCK's chance of survival.

Treatment options include:

  • Diet
  • Physiotherapy
  • Massage
  • Splinting
  • Surgery

For more details on how to care for a Flat Chested Kittens see the article titled, FCK: Treatment Options.

Note From The Author: This text is placed here to help breeders and owners who may come in contact with this distressing condition. Please note, I am not an expert, nor do I have veterinary training. I have gathered information from breeders who have experience of FCK to pass on to those who suddenly find themselves confronted with it but have no information on how to deal with it, and I would like to acknowledge all their contributions. Even the tiniest additional piece of information helps. This web-page is NOT a criticism of breeders or breeding - no good breeder will knowingly breed kittens who will get FCK.

Related Articles


  • Boudrieau R et al. Pectus excavatum in dogs and cats. Comp Contin Edu Pract Vet 12(3): 341-355, 1990
  • Fossum TW et al. Pectus excavatum in eight dogs and six cats. J Am Anim Hosp Assoc 25:595-605, 1989
  • McAnulty JF, Harvey CE. Repair of pectus excavatum by percutaneous suturing and temporary external coaptation in a kitten. J Am Vet Med Assoc 194(8): 1065-1067, 1989
  • Sturgess CP, Waters L, Gruffydd-Jones TJ et al. Investigation of the association between whole blood and tissue taurine levels and the development of thoracic deformities in neonatal Burmese kittens. Vet Rec 141:566-570, 1997

Back :: Top :: Home



Legal Disclaimer | Report A Broken Link or Typo

Website created & maintained by
ShowCatsOnline Web Design