Medically known as hyperthermia, heatstroke 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, however, they can overheat very easily. More so than humans, as panting isn't a particularly efficient way to cool down the animal.
The normal body temperature of a cat is 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 heatstroke is a very real possibility.
Heatstroke is a medical emergency which can lead to organ dysfunction, blood clotting disorders, coma, and death. It must be treated urgently.
- Rapid panting
- Bright red tongue
- Dark red gums
- Salivating (drooling)
- Muscle tremors
- Capillary refill time of less than 1 second. To test this, lift your cat's upper lip and place a finger on the gum applying a small amount of pressure. Remove your finger, and you should see the gum has turned white. Time how long it takes for the area to turn pink again.
- 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.
- Never leave your cat in a parked car, even in the cooler months, but this is especially important in hot weather. If you are travelling with your cat in the car, provide adequate ventilation or use the air conditioning.
- Provide shade. If your cat is allowed outside (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 him 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. Rooms with large windows or east facing rooms (in the Southern Hemisphere) tend to become hotter in afternoons so make sure your cat has access to cooler parts of the house. Cool flooring such as tiles and slate can offer relief. My dogs like to lie on the kitchen floor on hot days as it's away from the sun and has slate flooring.
- Drinking water. Always ensure your cat has an adequate supply of fresh, cool, clean water, indoors and outdoors. On warmer days, add some ice cubes and make sure you have more than one water bowl. Locate bowls out of direct sunlight.
- Avoid strenuous activity in high temperatures.
- Limit exposure to the outdoors in the hotter months. 11.00am and 3.00pm are the hottest times, so keep your cat indoors during this period.
- Keep the home cool with air conditioning or a fan. Keep your cat indoors during hot days, and if possible with the air conditioning or a fan turned on.
- Closing blinds or curtains can help to keep the room cool.
- Catsicles. Popsicles for cats can be a novel way to keep your cat cool when the heat hits. These can be made from lactose free cat milk (available from your supermarket) or canned cat food. Add milk or wet food to ice cube trays and freeze overnight. Take one or two frozen catsicles out as a cool treat.
- Cold water bottles. Fill old soft drink bottles with water (don't fill right to the top as water expands when it is frozen). Take out and wrap a towel around the bottle. Place where your cat sleeps.
- Glasshouses, sheds and garages can become extremely hot. Always check before closing doors to ensure your cat hasn't snuck in.
- Think for your cat. I have found that even on extremely hot days my cats won't always move themselves to a cooler part of the house, sometimes you have to do it for them.
Any cat can develop heatstroke however some are at greater risk.
- Brachycephalic breeds with short faces such as Persians, Himalayans and Exotics.
- Old cats.
- Very young cats.
- Sick cats.
- Obese cats.
- Cats with heart conditions.
- Cats with medical conditions which affect breathing.
- Pregnant and nursing queens.
Mild heatstroke (body temperature of 104°F or 40°)
- If the heatstroke 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, this will promote evaporative cooling.
- 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 the 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 heatstroke (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.
Some ways your veterinarian will treat your cat are as follows:
- Decrease body temperature. 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.
- Oxygen therapy will be given if your cat is having difficulty breathing.
- Intravenous fluids will be given to treat dehydration.
- Cortisone injections. Heatstroke can be associated with swelling in the throat, aggravating the problem. Your vet may give the cat a cortisone injection to treat this. 
- Monitoring. Your cat will be carefully monitored for signs of kidney or liver failure or disseminated intravascular coagulation.
Cats who have suffered heatstroke are at greater risk of developing 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.
Updated 14th January 2017.