What is heat stroke?
Also known as 'hyperthermia', heat stroke is a life threatening medical condition in which the body's internal organs (liver, kidneys, lungs, heart and brain) begin to shut down as a result of elevated body temperature caused by high temperatures and humidity.
Cats protect themselves against high temperatures by panting and licking their fur and can overheat very easily. More so than humans as panting isn't a particularly efficient way to cool down the animal.
The cat's body temperature is approximately 100.5 to 102.5 degrees Fahrenheit, or 38.2 to 39.2 Celsius. If the outside temperature is warmer than the cat's internal temperature heat stroke is a very real possibility. Heat stroke is a medical emergency which can lead to organ dysfunction, coma and death and must be treated urgently.
What are the symptoms of heat stroke?
- Rapid panting
- Bright red tongue
- Dark red gums or pale gums
- Salivating (drooling)
- Muscle tremors
- Capillary refill time of less than 1 second
- Vomiting (possibly with blood)
- Diarrhea (possibly with blood)
- Bleeding from the nose (this is indicative of disseminated intravascular coagulopathy [DIC]), which is a condition in which the blood clotting system fails.
How to avoid heat stroke in cats:
- Never leave your cat in a parked car, even in the cooler months, this is especially important in hot weather. If you are travelling with your cat in the car, provide adequate ventilation.
- If your has access to the outdoors (either free to roam or in an enclosure) make sure they have access to a shaded area where they can escape from the sun and heat.
- If your cat is indoors only, give it access to a cool area. It is especially important not to confine the cat to any room where temperatures are especially high, such as a sunroom.
- Always ensure your cat has an adequate supply of fresh, cool, clean water, indoors and outdoors.
- Avoid strenuous activity in high temperatures.
- Limit exposure to the outdoors in the hotter months between 11.00am and 3.00pm.
- Keep your cat indoors during hot days, and if possible with the air conditioning or a fan turned on.
Who's at risk?
Any cat can develop heat stroke however some are at greater risk.
- Short faced breeds such as Persians.
- Old cats.
- Young cats.
- Sick cats.
- Obese cats.
- Cats with heart conditions.
- Cats with medical conditions which affect breathing.
- Pregnant and nursing queens.
Should I treat my cat at home and how?
Mild heat stroke (body temperature of 104°F or 40°)
If the heat stroke is mild, you may be able to bring the cat's temperature down at home by wrapping him in cool, wet towels or immersing him in cool (but not cold) water. Keep water away from the mouth and nose.
Apply ice packs or frozen vegetables to the head and between the legs.
Put rubbing alcohol on the cat's paws and legs to assist in bringing the temperature down.
If you have a fan or air conditioning turn this on, evaporation will help cool the cat.
Keep your cat in a cool place.
Offer plenty of cool, fresh water.
Once the body temperature has returned to normal, stop cooling or you may cause hypothermia in your cat. Monitor your cat's rectal temperature, every 5 - 10 minutes. Once you have brought your cat's temperature down take him to the vet. The cat may appear to be over the incident, but damage may have been caused to the organs, so it is always recommended your cat is given a check over by a veterinarian.
Moderate to severe heat stroke (body temperature is 105F or 40.5C)
Take the cat to the vet immediately. If possible, have somebody else drive, while you attempt to bring down the temperature on the way via the above methods.
How will my veterinarian treat heat stroke in my cat?
Some ways your veterinarian will treat your cat are as follows:
Your veterinarian will carefully bring your cat's body temperature down to a safe level. He will introduce cool fluids to the body either intravenously or by administering a cool water enema.
The cat may be given oxygen if he is having breathing difficulty.
Fluids to treat dehydration.
Heat stroke can be associated with swelling in the throat, aggravating the problem. Your vet may give the cat a cortisone injection to treat this. 
Your cat will be carefully monitored for signs of organ damage.
Cats who have suffered heatstroke are at greater risk of getting it again. So it is important to take the necessary steps to avoid this.
Carefully monitor your cat's health for signs of possible long term damage caused by the heatstroke and speak to your veterinarian if you see anything unusual.
Watch for blood in the urine.
Your veterinarian may prescribe a special diet which will put less strain on the damaged kidneys.
 Cat Owner's Home Veterinary Handbook by Delbert G. Carlson and James M. Giffin.