Heatstroke in Dogs: How to Recognize the Signs and What to Do

In brief

There are four things you should know about heatstroke in dogs. First, the most common trigger is not the hot car but exercise: in a British analysis of more than 900,000 dogs, 74.2 percent of cases with a known trigger were due to exertion, and 5.2 percent to the car. Second, where the type of exertion was recorded, two thirds of these cases happened after an ordinary walk, not during sport. Third, the widespread warning against cold water is now considered refuted – veterinary guidelines explicitly recommend cold water. And fourth, the rule is “cool first, then drive,” not the other way around.

Heatstroke develops faster than most owners expect, and the common advice on it is outdated on one central point. This article explains how to recognize early warning signs, what actually helps in an emergency – and why the most common source of danger is the one hardly anyone thinks about.

👉 The basics of preventive care and health checks for your dog

1. What happens during heatstroke

Dogs shed heat mainly by panting. Sweat glands in the paws play only a minor role in regulating body temperature. On hot days, during physical exertion, or in poorly ventilated rooms, this mechanism quickly reaches its limit.

A word on terminology, because it often gets muddled: hyperthermia simply means an elevated body temperature. Heatstroke is the term used when this overheating triggers a progressive, body-wide inflammatory response and dysfunction of several organ systems – with neurological deficits and the possibility of a fatal outcome. Body temperatures from about 41 °C upward are considered the critical range.

What then happens in the body:

• Circulatory failure
• Oxygen deprivation in the tissues
• Organ damage to the liver, kidneys, and brain
• Damage to the intestinal lining, with vomiting and bloody diarrhea
• Breakdown of muscle tissue, which in turn puts strain on the kidneys
• Blood clotting disorders

An important distinction: overheating from outside is not the same as fever. With fever, the body resets its own set point, usually as a result of an infection. In heatstroke, that trigger is missing – the heat comes from outside or from muscle work, and the body cannot get rid of it fast enough.

2. Recognizing the symptoms

Symptoms at a glance – the more signs appear at the same time, the more urgent it is to act.

2.1 Reading panting correctly

Panting is the cooling mechanism and therefore not an alarm sign in itself. The question is which kind of panting you are looking at – and this is where early recognition most often fails.

Unremarkable: panting that starts after exertion and eases off within a few minutes of rest. The tongue stays its normal width, the mouth relaxed.

Concerning: panting that does not ease despite a break in the shade. A tongue that is widened, stuck far out, and looks curled at the edges. An outstretched neck with the mouth wide open. Noises that weren’t there before.

And the point most often misread: panting that suddenly stops without the dog having recovered is not a good sign. An exhausted dog that goes quiet and lies down may have calmed down – or may be in a phase that can quickly turn dramatic. The difference shows in the gums and in how responsive the dog is, not in the quiet.

About the gums: normal is pale pink and moist. Bright red suggests overheating; pale or bluish suggests a circulation problem. If you press briefly with a finger, the color should return within about two seconds.

This check takes five seconds and, when in doubt, tells you more than any time of day or temperature reading.

3. Taking the temperature – and what the number means

The previous section gives temperature values, and the next one asks you to keep measuring while you cool. Both assume that you know how to do it – and that you know what the number tells you.

3.1 How to measure

Only rectal measurement is reliable. Ear thermometers are inaccurate in dogs, and what you feel on the belly or the ears tells you nothing about core temperature.

In practice: a digital thermometer, a little lubricant or petroleum jelly, insert the tip a few centimeters, wait for the beep. It takes seconds. A second person keeping the dog busy at the head end makes it easier.

And the point that decides the emergency: you practice this when nothing is going on. A dog that meets the thermometer for the first time during heatstroke will resist – and then nobody measures anything.

3.2 What the values mean

The normal range is roughly between 37.5 and 39 °C, slightly higher in puppies. After exertion, a raised value is normal and comes back down with rest.

From about 39.5 °C, attention is warranted; from about 41 °C, the critical range from section 1 begins. What matters is not the number alone but what the dog is showing along with it: a lively dog at 39.8 °C after a walk is a different matter from a staggering one with the same reading.

3.3 Why measuring matters while you cool

Cooling without monitoring carries its own danger: the temperature can drop below the normal range, and hypothermia makes the situation worse. That is why the guidelines state that active cooling should be stopped as soon as the normal range is reached.

If you can’t measure, cool anyway – that is clearly better than waiting. But then head to the clinic promptly and tell them how long you cooled.

A thermometer therefore belongs in every first-aid kit at home and, in the warm months, in the car. It costs very little and, in an emergency, is the only piece of information that isn’t based on guesswork.

4. First aid: the point where many guides get it wrong

Here this article has to correct a widespread recommendation – including what many popular guides still say.

The rule is: cool first, then transport. That is what the veterinary guidelines on the first-line care of dogs with heat-related illness, published in 2016, say. They recommend two methods: immersion in cold water, and evaporative cooling – that is, getting water onto the dog while making sure air is moving over it (Hall et al., 2023).

The same analysis shows how rarely this is done: of 341 cases with documented cooling, only 74 – that is, 21.7 percent – had been cooled before transport.

Why cold water is right

The argument that you must not use cold water because the blood vessels in the skin constrict and the heat then stays trapped inside the body is one of the most persistent pieces of misinformation in this field. It sounds plausible but does not hold up to scrutiny: in human and equine sports medicine, this concern is considered refuted, and active cooling with cold water or evaporative cooling is described there as the most effective treatment for severe overheating. For humans, cold-water immersion at water temperatures of roughly 1.7 to 15 °C is considered the standard for exertional heat illness (Hall et al., 2023).

Germany’s national veterinary chamber says the same. The Bundestierärztekammer (German Federal Chamber of Veterinarians) summarizes the guideline of the Veterinary Committee on Trauma as follows: the overheated animal should be cooled before it is transported for emergency veterinary care – in young and healthy dogs, immersion in cold water has proven particularly effective, while for older animals and those with pre-existing conditions, evaporative cooling is recommended, that is, spraying skin and coat combined with air movement (Bundestierärztekammer, 2024).

So if you read elsewhere that you should only use lukewarm water: that recommendation is outdated.

In practice, this means:

Use cold water. Don’t wait to find the “right” lukewarm water. Use whatever cold tap water or natural water is available. What matters is starting to cool immediately – a stream, a garden hose, a tub, a bucket.

Cool the whole dog, not just the paws. The advice to wet only the paws and legs wastes cooling surface. Pour water over the whole body, or immerse the dog if a safe body of water or container is available. Keep the head clear.

Get air moving. Water plus airflow cools much better than water alone.

A wet towel laid over the dog is not a reliable cooling method on its own. In practice it is the most commonly used method, yet it is not one of the recommended ones. The reason lies in how it is used: a towel lying snugly on the dog warms up quickly and can then hinder heat loss instead of helping it.

That doesn’t make a towel useless – it depends on how it is used. It makes sense as a wet mat for the dog to lie on, or if it is changed frequently while you keep air moving. It is unsuitable as a wrap that stays on the dog for hours. And in no case does it replace pouring water over the dog or immersing it, as described in the points above.

One caveat belongs here: the recommendation for cold-water immersion refers to young, healthy dogs with stable circulation – that is, dogs that are responsive, can stand, and have pink mucous membranes. What matters is the dog’s condition in the moment, not age alone: a ten-year-old dog that is alert and circulatory-stable is a different case from a three-year-old that is staggering and has pale mucous membranes.

For animals with impaired consciousness, collapsed animals, or those with unstable circulation, as well as dogs with known heart or respiratory disease, evaporative cooling is preferred – water plus air movement. It is somewhat slower and much easier to control.

The steps

1. Stop the exertion immediately and get out of the heat. Shade or a cool room. No more walking, not even “just back to the car.”

2. Cool – immediately and on the spot. Cold water over the whole body, plus air movement. Don’t get into the car first.

3. Offer water, don’t force it. Small amounts, fresh. A dog with impaired consciousness must not be given anything to drink – risk of choking and aspiration.

4. Check the temperature if possible. Measure rectally and keep track while cooling. When body temperature returns to the normal range, active cooling should be stopped to avoid hypothermia.

5. Call and drive. Call the practice or clinic ahead so they can prepare. Pre-cool the car, put the dog on the floor rather than the seat, keep cooling during the drive, no closed crate.

6. Go even if the dog seems to recover. Organ damage can show up hours later.

4.1 What should be prepared

The steps above assume that water and a way to the clinic are available. Both can be prepared, and in summer it pays off.

In the car: a water canister, a thermometer, a large bowl or a collapsible bucket. A canister in the trunk is the difference between cooling right away and first having to look for water.

On the walk: water for the dog and, if possible, knowing where the streams, ponds, and fountains along the way are. If you know where the nearest water is, you save minutes in an emergency.

In your head: the number of your own veterinary practice and of the nearest emergency clinic, saved in your phone. Plus knowing how far it is – the call during the drive is step 5 from the list above.

And the point hardly anyone thinks about: if you are out alone, you cool and phone at the same time. If there are two of you, you split the tasks. On an outing with several dogs, it’s worth agreeing on this beforehand – just as you would agree on who does what if a scuffle breaks out.

The effort is small. What sets heatstroke apart from other emergencies is that the most effective measure here really is in the owner’s hands rather than the clinic’s – and that it needs water.

5. What happens at the vet

So that it’s clear why the visit is necessary even if the dog seems to recover.

Immediate care. IV fluids stabilize the circulation and replace lost fluids. Lowering the temperature is continued in a controlled way and monitored.

Organ checks. A blood count and blood chemistry show whether the liver, kidneys, or blood clotting are affected. Because damage can develop with a delay, hospitalization for observation is often necessary.

Further treatment depending on findings. Which medications are used depends on the clinical picture and the lab results.

Heatstroke is only over when the values are stable – not when the dog is back on its feet.

6. The days after

The sentence from the previous section – it’s over when the values are stable, not when the dog is standing again – deserves some explanation, because this is where the second critical period lies.

6.1 Why things can still get worse later

Damage to the liver, kidneys, intestines, muscles, and blood clotting does not always show right away. A dog can seem responsive again after cooling and then deteriorate over the following one to three days. That is exactly why dogs are examined, and often kept in the hospital for monitoring, even when they appear to have recovered.

What to watch at home: appetite, vomiting, diarrhea – especially with blood in it –, how much the dog drinks and urinates, dark or coffee-colored urine, pale gums, pinpoint bleeding on the mucous membranes or the skin of the belly, lethargy, staggering, or changed behavior.

Any of these is a reason to call immediately, even at night.

6.2 Returning to everyday life

How long the dog needs to take it easy is decided by the veterinary practice – it depends on the extent of the damage, not on gut feeling. What applies in every case: no exertion while values are still being checked, and after that a gradual build-up rather than the usual walk on the first nice day.

6.3 A point that surprises owners

A dog that has had heatstroke once is considered more at risk of another one. Whether that is due to a lasting impairment of heat regulation or to the same circumstances coming together again has not been conclusively settled – in practice, both amount to the same thing.

For this dog, that means the measures from section 8 are no longer optional from now on, and the incident belongs in the medical record so that it is taken into account at future appointments in summer.

7. Where the danger actually comes from

A close look pays off here, because public perception differs markedly from the data.

In the largest study on this to date, the treatment records of 905,543 dogs in British primary veterinary care were analyzed and 1,259 heat-related illness events identified. Among the cases with a known trigger, the breakdown was as follows (Hall et al., 2020):

• Exertion: 74.2 percent
• Environmental heat: 12.9 percent
• Confinement in a vehicle: 5.2 percent
• Treatment at the vet or the groomer: 4.6 percent
• Confinement in buildings: 2.7 percent

And now the finding that changes prevention: of the exertional cases in which the type of exertion was recorded, 67.5 percent occurred after a walk. Only 17.6 percent followed intense activities such as running or cycling, and 13.8 percent followed play.

So the typical case is not the dog forgotten in the car, and not the dog pushed too hard in sport. It is an ordinary walk in weather that is too warm.

Two further points from the same analysis: exertional cases occurred in every month of the year. And the risk of death did not differ statistically between triggers – but exertional cases affected around ten times as many dogs and led to roughly eight times as many deaths as the vehicle.

That does not diminish the warning about the hot car. A parked car heats up to life-threatening levels within a short time, even with a window cracked and in the shade, and there is no safe version of it. But if that is all you think about, you overlook three quarters of the risk.

How to adapt everyday summer life as a whole is covered in our guide Summer heat and your dog.

8. Prevention

Take the walk itself seriously as a risk. This is the most important change compared with the usual summer advice. On warm days, it is not only intense training that is too much – the usual walk can be too. Shorten it, move it, or skip it and replace it with calm activities somewhere cool.

Change the timing. Early in the morning or late in the evening. The common rule of thumb of avoiding midday and the afternoon is a useful guide – but what matters is the actual conditions where you are, not the time on the clock.

Choose your routes. Woods, shady paths, water along the way.

Check the paws. Hot asphalt can cause burns. The common hand test – the back of your hand or your palm on the surface for a few seconds – is not a calibrated method, but it is a sensible rule of thumb: too hot for you, too hot for your dog. The paw pads, however, are not a reliable indicator of the dog’s overall heat load – a cool forest floor does not protect against the walk as a whole being too much.

Train a stop signal and recall. This is where training concretely prevents emergencies: many dogs do not regulate themselves in the heat. A ball-crazy dog or one with a strong drive to hunt often won’t stop on its own just because it is too warm – it stops when you can call it off. A reliable recall and a properly built stop signal are safety equipment in the heat, not a matter of obedience.

Bring water. Every time you go out.

Provide cool places to lie down. Create retreats at home and make sure air is moving.

Think about the vet and the groomer. Veterinary treatment and grooming were the fourth most common trigger in the analysis. Both are warm, often stressful environments. For dogs at risk, it is worth booking appointments at cool times of day and actively raising the topic.

Never leave your dog in a parked car. Not even briefly.

8.1 When is it too warm? The question behind the question

“At what temperature should I stop going out?” is the most common question on this topic – and it can’t be answered with a single number. What counts is the combination of five factors.

Humidity. It is almost always forgotten, and it is decisive: dogs cool themselves through evaporation while panting. When the air is humid, less evaporates – 24 degrees in muggy air can be more taxing than 28 degrees in dry air.

Ground temperature. Asphalt stores heat and radiates it back, and the dog walks twenty centimeters above it. The official air temperature is measured at a height of two meters.

What has already happened that day. A dog that already had a walk at midday doesn’t start from zero in the evening.

The dog itself. Age, weight, head shape, coat, pre-existing conditions – the differences described in section 10 are considerable.

And what happens on the walk. The same 26 degrees means something different on a calm sniffing walk than with dog encounters and ball games.

A useful rule of thumb instead: if you imagine jogging the route in your street clothes and that sounds unpleasant, it is too much for your dog. And when in doubt, follow the order from section 8 – shorten, move, or replace.

9. The dog that doesn’t slow itself down

The finding from section 7 – two thirds of the exertional cases after an ordinary walk – has a flip side that falls within our responsibility: many dogs don’t stop when it gets to be too much.

9.1 Why self-regulation fails

A dog in prey-driven behavior, playing with other dogs, or anticipating the ball is highly aroused. In this state, many dogs keep running even though they are already overheating.

The same applies to dogs that are strongly oriented toward their person, and to those that have learned that the walk only ends after a certain distance. The idea that a dog will lie down on its own when it gets too warm holds true for some dogs – and probably least of all for the at-risk dogs from section 10.

9.2 What follows from this

The decision is yours, not your dog’s. In the heat, exertion is limited in advance, not cut short once signs appear. If you wait for signs, you have already passed the early stage from section 2.

No ball throwing, no long play sessions with other dogs. These are the two situations in which arousal and exertion combine most strongly.

Recall and the stop signal are safety equipment here. A dog that will stop mid-motion can be halted before something happens. This is not a question of obedience but the difference between a walk with an emergency and one without.

And water is no substitute for a break. A dog that drinks from the stream and keeps running has had a drink – it has hardly cooled down.

9.3 Swimming and cooling off on the way

Swimming is a good option as long as the water is safe. Two caveats belong with it: retrieving in water is exertion, not recovery – a dog that spends an hour fetching dummies out of a lake can overheat despite the water. And warmed-up shallow water in high summer hardly cools at all.

The more sensible approach is therefore the unspectacular one: shade, rest, a wet mat, air movement – and walks scheduled for the cool times of day.

10. Who is particularly at risk

The risk profiles differ depending on the trigger – which matters in practice, because it explains why the athletic, healthy dog can be affected too (Hall et al., 2020).

For exertional heatstroke:

• Young dogs. Dogs over eight years old had lower odds of an exertional case than dogs under two.
• Larger and heavier dogs. All weight classes from 10 kg up had higher odds than dogs under 10 kg; so did dogs at or above the average weight for their breed and sex.
• Males and neutered females compared with intact females.
• Active working and family breeds. Labrador Retrievers had 2.1 times the odds of mixed breeds; Boxers, Golden Retrievers, and Border Collies were similar. Purebred dogs overall had 1.84 times the odds of mixed breeds.

For environmental heat:

• Old dogs. From twelve years of age, 3.15 times the odds of dogs under two.
• Short-headed dogs (brachycephalic breeds) have an increased risk (2.36 times that of dogs with a medium-length muzzle); the obvious explanation is their limited ability to shed heat by panting. In bulldogs, it has been observed that they can overheat just from standing in a room at 21 °C.

For vehicles: short-headed dogs had 3.07 times the odds. As a basic rule here, though: any dog overheats in a hot car once the surrounding temperature exceeds its body temperature.

What this means for you: if you have a young, strong, active dog, you are not the exception for the most common form – you are the target group. And if you have a short-headed dog, you are at increased risk for all three forms.

11. What follows from the risk profiles

The figures in the previous section are unusual because they contradict expectations – and that is exactly why it is worth translating them into action.

11.1 The young, athletic, large dog

This dog is the typical case of exertional heatstroke, not the old or short-headed dog. Labradors, Boxers, Golden Retrievers, and Border Collies were clearly above the risk of mixed breeds.

What follows: with these dogs in particular, the assumption “he’s fit, he can handle it” is misleading. Fitness extends the time until exhaustion – it does not protect against overheating. A trained dog often runs faster and longer and in doing so produces more heat overall.

11.2 The old and the short-headed dog

They rank high for a different trigger: environmental heat. For them, the main problem is not the walk but the top-floor apartment, transport, the waiting room, the grooming salon.

What follows: for these dogs, how you set up their surroundings matters more than how you plan the walk – a cool retreat, air movement, appointments booked for the early hours.

11.3 And what applies to everyone

That exertional cases occurred in every month of the year is the finding with the greatest practical reach. A mild April day with a long walk and an overly motivated dog is enough. The idea that the issue starts in June and ends in August is not true.

11.4 Limits of the evidence

On the nature of the evidence: the frequency and risk figures come from an analysis of documented treatment visits in British primary veterinary care. That is a large population, but it reflects what is in the records – cases that stayed at home because the dog recovered are missing. The true frequency is therefore likely to be higher, and the documented cases tend to be the more severe ones.

Second, the proportions by trigger refer to cases with a known trigger. Where nothing was noted, the case is not counted in any of the groups.

Third, risk figures such as “2.1 times the odds of mixed breeds” are ratios, not probabilities for the individual dog. A raised multiple of a small baseline risk is still a manageable risk – the figures tell you where attention is worthwhile, not that a Labrador will get heatstroke this summer.

And fourth, the data are British. Climate, husbandry habits, and breed distribution differ; the orders of magnitude are transferable, the exact proportions not necessarily.

What remains unaffected by all this: the first-aid recommendations. They come from veterinary guidelines and from human and equine sports medicine, and they do not depend on these frequency figures.

12. Conclusion

Heatstroke is an emergency – and in most cases preventable, because it depends on human decisions.

The three things that make the difference:

Take the walk seriously. The most common trigger situation is not an extreme one, but the usual walk in weather that is too warm.

Cool first, then drive. With cold water, over the whole body, with air movement – not with wet towels, and not only once you reach the clinic.

Always have it checked. Even if the dog has recovered.

If you are unsure about the warning signs: call the practice and describe what you are seeing. It costs nothing and, in an emergency, saves the minutes that count.

If you take only one thing away from this article: when heatstroke is suspected, you cool first and then drive – with cold water, over the whole body, right there on the spot. That is the order that was followed in only about one in five cases with documented cooling in the analysis, and it is probably the most effective single decision in this whole topic.

Key takeaways on heatstroke

The most common trigger is exercise, not the car. In an analysis of 905,543 dogs, 74.2 percent of cases with a known trigger were due to exertion, 5.2 percent to the vehicle (Hall et al., 2020).

It is usually the ordinary walk. Where the type of exertion was recorded, 67.5 percent occurred after a walk – only 17.6 percent after intense activity.

The warning against cold water is outdated. Veterinary guidelines explicitly recommend cold water; the concern about constricted skin blood vessels is considered refuted.

Cool first, then drive. In the analysis, only 21.7 percent of 341 documented cooling cases had been cooled before transport.

A wet towel laid over the dog does not cool reliably on its own. It is the most commonly used method and yet not one of the recommended ones – lying snugly on the dog, it warms up quickly and can hinder heat loss. As a wet mat or when changed frequently, on the other hand, it is useful.

Cold-water immersion requires a dog with stable circulation. What matters is the dog’s condition in the moment, not age alone – for animals with impaired consciousness, collapsed or unstable animals, evaporative cooling is preferred.

Cool the whole dog, not just the paws – and stop active cooling as soon as the normal range is reached, to avoid hypothermia.

Exertional cases occurred in every month of the year. And they affected around ten times as many dogs as the vehicle, with roughly eight times as many deaths.

It’s over when the values are stable – not when the dog is back on its feet. Damage to the liver, kidneys, intestines, muscles, and clotting can show up with a delay.

References

• Bundestierärztekammer. (2024, July 15). Notfall: Hitzschlag beim Hund. https://www.bundestieraerztekammer.de/presse/2024/07/Hitzschlag-beim-Hund.php
• Hall, E. J., Carter, A. J., & O'Neill, D. G. (2020). Dogs don't die just in hot cars – Exertional heat-related illness (heatstroke) is a greater threat to UK dogs. Animals, 10(8), Article 1324. https://doi.org/10.3390/ani10081324
• Hall, E. J., Carter, A. J., Bradbury, J., Beard, S., Gilbert, S., Barfield, D., & O'Neill, D. G. (2023). Cooling methods used to manage heat-related illness in dogs presented to primary care veterinary practices during 2016–2018 in the UK. Veterinary Sciences, 10(7), Article 465. https://doi.org/10.3390/vetsci10070465
• Hall, E. J., Carter, A. J., & O'Neill, D. G. (2020). Incidence and risk factors for heat-related illness (heatstroke) in UK dogs under primary veterinary care in 2016. Scientific Reports, 10, Article 9128. https://doi.org/10.1038/s41598-020-66015-8
• Lilja-Maula, L., Lappalainen, A. K., Hyytiäinen, H. K., Kuusela, E., Kaimio, M., Schildt, K., Mölsä, S., Morelius, M., & Rajamäki, M. M. (2017). Comparison of submaximal exercise test results and severity of brachycephalic obstructive airway syndrome in English bulldogs. The Veterinary Journal, 219, 22–26. https://doi.org/10.1016/j.tvjl.2016.11.019

Note: This article does not replace a veterinary examination or treatment. If you suspect heatstroke, start cooling immediately and contact your veterinary practice or an emergency veterinary service without delay.

Frequently asked questions about heatstroke in dogs

How to recognize symptoms early, respond correctly, and protect your dog from overheating