What is the most common cause of heatstroke in dogs?

Exercise in the heat, not hot cars. A large UK study found about 74 percent of heat-related illness in dogs was triggered by exertion, versus only about 5 percent from being left in a vehicle. Both are dangerous, but the everyday risk is over-exercising a dog when it is hot.

What are the signs of heatstroke in a dog?

Heavy, frantic panting, drooling, bright red gums, weakness or collapse, vomiting or diarrhea (sometimes bloody), disorientation, and in severe cases seizures and organ failure. A normal dog temperature is about 100.5 to 102.5°F; heatstroke generally means a core temperature of 105°F or higher with these signs.

How do I cool a dog with heatstroke?

Start cooling immediately, before driving to the vet (cool first, transport second). Pour or spray water that is cooler than the dog over its body and move air across it with a fan or breeze. Current guidance favors cold water rather than only tepid water, and for young, fit dogs, cool-water immersion. Then get to a vet even if the dog seems to recover.

Which dogs are most at risk of heatstroke?

Flat-faced (brachycephalic) breeds are at much higher risk, as are overweight dogs, older dogs, dogs with airway disease, and any dog exercising hard in heat and humidity or left in a hot space. Flat-faced breeds also have a higher risk of a fatal outcome.

Can a dog recover from heatstroke?

Many do, especially milder cases, but severe heatstroke is deadly: while overall survival among dogs brought to vets is high, only around 43 percent of severe cases survive. Fast cooling and prompt veterinary care, plus watching for delayed organ damage, give the best chance.

Heatstroke in Dogs: The Emergency That Is Mostly About Exercise, Not Hot Cars

Here is the short version: heatstroke is a true killer, and the popular image of it, the dog in the parked car, is the least common cause. Most dogs that overheat do so while exercising in the heat. The disease can damage every organ in the body, and the best-evidence first aid has actually shifted in recent years toward cooling the dog hard and fast before you even leave for the vet. This guide covers who is at risk, the warning signs, the updated cooling guidance, and how to prevent it.

It is mostly about exercise, not cars

This is the finding that should reshape how owners think about heat. In a large UK study of dogs, about 74 percent of heat-related illness was exertional, triggered by exercise, while environmental heat accounted for around 13 percent and being left in a vehicle only about 5 percent.¹ Hot cars are real and deadly, and we will get to them, but the everyday danger is taking a dog for a hard walk, run, or game of fetch on a hot, humid day. The title of that study says it plainly: dogs don't die just in hot cars.¹

~74%

of heat-related illness in dogs is triggered by exercise, versus only ~5% from hot cars

Hall et al., Animals, 2020 (UK VetCompass data)

Which dogs are most at risk

Some dogs are far more vulnerable than others.⁵ Flat-faced brachycephalic breeds (Bulldogs, Pugs, French Bulldogs and the like) top the list, with roughly double the odds of heat illness and a notably higher chance of a fatal outcome, because their airways make it hard to pant off heat efficiently. Other strong risk factors are being overweight, older age, and airway or laryngeal disease. Heat plus humidity, hard exercise, a thick coat, and a lack of acclimatization all add to the load. If you have a flat-faced or heavy dog, the threshold for caution should be much lower.

The signs, and the temperature line

A normal dog's body temperature is about 100.5 to 102.5°F. Heatstroke generally means a core temperature of 105°F or higher accompanied by clinical signs.³ Watch for:

Heavy, frantic panting and heavy drooling.
Bright red gums.
Weakness, stumbling, or collapse.
Vomiting or diarrhea, sometimes bloody.
Disorientation, and in severe cases seizures.

Severe heatstroke can progress to kidney failure, clotting problems, and multi-organ damage, which is why it is a true emergency even after the dog cools down.³

First aid: cool first, transport second

Here is where the advice has genuinely changed, and it matters. The instinct is to bundle the dog into the car and drive to the vet. Current guidance from the Royal Veterinary College flips that order: cool first, transport second, because how quickly the dog's temperature comes down strongly affects the outcome.²

The other shift is about water temperature. The old advice to use only tepid, never cold, water is now considered outdated. The RVC's guidance is to cool the dog using water that is cooler than the dog, and that colder is better, using whatever you have. For young, otherwise-healthy dogs, especially after exertion, cold-water immersion is recommended. For older dogs or those with health problems, pour cool water over the body and move air across it with a fan or breeze. Wet towels laid on the dog are the least effective method, so do not rely on them alone.²

Then, crucially, take the dog to a vet even if it seems to recover, because dangerous organ damage can show up hours later.³

How deadly it is

Heatstroke earns its emergency status. While most dogs brought to a vet for heat-related illness survive, the picture darkens fast with severity: only around 43 percent of severe cases survive.⁵ In other words, a mild overheating episode handled quickly usually ends well, but a dog that reaches true, severe heatstroke is in genuine danger, which is exactly why fast cooling and prevention matter so much.

Why hot cars still deserve the warning

Even though cars cause a minority of cases, they remain lethal because of how fast they heat. On a 70°F day, the inside of a parked car climbs about 20 degrees in 10 minutes and more than 40 degrees in an hour, and cracking the windows makes essentially no difference.⁴ The rule is simple and absolute: never leave a dog in a parked car.

What to do this week

On warm or humid days, move walks and play to the cool early morning or evening, and keep exertion light, especially for flat-faced or heavy dogs.
Make a cooling plan now: know that you will wet the dog with cool water and move air before driving, so you are not improvising in a panic.
Always provide shade and water outdoors, and never leave a dog in a parked car for any length of time.
If you have a brachycephalic or overweight dog, treat heat as a serious risk and watch closely for early heavy panting that will not settle.

Heatstroke is both deadly and, for the most part, preventable, and the research points the finger squarely at how we exercise dogs in the heat rather than at careless car owners alone. Time your activity, respect your dog's breed and build, and learn the cool-first response cold. For a dog in trouble on a hot day, the minutes you spend pouring on cool water before you drive may be the most important minutes of all.