Recognising heatstroke in dogs and responding correctly

It is one of those shimmering afternoons when the patio slabs grow as hot as a stovetop. In the garden a young bulldog dozes in the shade — moments ago he was still chasing a ball with abandon. But now his panting sounds different: fast, shallow, the tongue hanging out broad and low. When his owner calls him, he only lifts his head wearily and stays put.

Something is wrong. And what happens in the next twenty minutes decides whether this dog will spend the evening back in the garden.

The good news first: anyone who knows a few things — and has prepared them — holds very good cards. That is exactly what this is about, told through an ordinary summer’s day and backed by research and a veterinary university. Read only the story if you like; if you want to know exactly, the studies are there for it.

Important: This text is no substitute for veterinary advice. It helps with recognition and first aid — diagnosis and treatment belong in veterinary hands. Whenever heatstroke is suspected, the rule is always: cool the dog and go to the vet immediately — even if he looks okay again after cooling down. This is vital!¹

The first move: recognising it

The owner kneels down beside him and does the right thing almost without thinking: she lifts the lip and presses briefly on the gum with a finger. Normally it would be pink, moist and glossy, and the white pressure mark should turn pink again within two seconds. In his case it takes longer; the mucous membrane looks dull.² A warning sign.

Heatstroke can be graded by severity. The peer-reviewed VetCompass grading scheme sorts the signs like this:³ mild means lethargy or stiffness and heavy panting; moderate adds vomiting or diarrhoea, heavy drooling, a transient collapse or a single seizure; it becomes severe with disturbances of the nervous system — staggering, multiple seizures, clouding of consciousness up to unconsciousness — as well as organ failure and clotting disorders.

In the young bulldog it is altered panting, listlessness and the delayed refill time — mild by the scheme. But mild is not harmless: the damage is done by the duration of the overheating, not first by drooling or collapse. Anyone who waits for those waits too long.

And the thermometer? It helps only in second place. When Hall and colleagues developed their grading scheme in 2021, they deliberately left body temperature out as a sole criterion: it is the duration of the overheating that does the damage — a single reading on its own says little.³ In other words: the signs are what count, not a single number. If you can measure, measure — but never wait for it.

“Where is the emergency card?!”

It is the sentence that comes up in exactly these moments — and usually the answer is: somewhere. Not for this owner. For weeks a printed card has hung on the fridge door, right next to the emergency numbers for the people in the house. On it are the steps and the number of the nearest 24-hour clinic. No searching, no googling with shaking fingers.

She tears the card off the magnet, phones the clinic on her way past (“Suspected heatstroke, we’re coming right now”) and is already heading outside to the garden hose. Preparation buys exactly the minutes that matter here. How to get hold of this card is explained further down — it takes five minutes and can save a dog’s life.

Short nose, short time

That it happened so fast is no accident. Dogs barely sweat; their most important cooling is panting — and that fails early: above just 28 °C ambient temperature, panting-based cooling is already impaired.² In short-nosed (brachycephalic) breeds there is an added problem: the shortened muzzle worsens heat loss through panting — the greatly reduced surface area of the upper airways makes evaporative cooling less effective.⁴

These are exactly the dogs it hits hardest. One of the largest investigations — a VetCompass study by Emily Hall, Anne Carter and Dan O’Neill, 2020, analysing 905,543 dogs in UK primary care — found the highest risk in the Chow Chow, the Bulldog and the French Bulldog; raised too by excess weight and with increasing age.⁵ The Old English Bulldog — like our Amadeus — also counts as a short-nosed breed within this group (though less extreme than the English Bulldog): brachycephaly is an independent, documented risk factor.⁵ The University of Veterinary Medicine Hannover names the same groups and adds dogs with respiratory disease as well as those that have already had a heatstroke.² And so that it is clear how serious this is: in the UK analysis, one in seven recorded heatstroke events ended in death (14.18 %).⁵

Young and healthy — so into the cold-water bath

Now one more detail matters: he is young and otherwise healthy. That determines how to cool. For young, healthy dogs the cold-water immersion bath is the fastest method; for old or pre-diseased animals, evaporative cooling (dousing plus air flow). What differs is the method, not the temperature — cool to cold applies to both.⁶ One thing holds for both: the water must reach right down to the skin. If only the topcoat gets superficially wet, the dense fur beneath acts like an insulating layer — it traps the heat instead of releasing it. The dog looks cooled but keeps overheating. So: soak it through and provide air flow.⁷⁶

Our owner opts for the immersion bath, and in this case that is exactly right.

This is how first aid proceeds:

1. Straight into the shade / a cool room.²
2. Cool over a large area with cool to cold water — body, legs, paws — and provide air movement. Start at once with whatever cold water is to hand; every delay worsens the outcome.⁶
3. If possible, measure the temperature rectally and stop active cooling as soon as it approaches the normal range (38–39 °C) again — overcooling is to be avoided.²
4. Offer water only to the responsive dog — never force it.²
5. Cool first, drive second⁶: to the vet as fast as possible; for the car, soak the fur, wind the windows down and set off immediately so the trapped heat can escape. As soon as the air conditioning cools, turn it up full and close the windows.²⁷

The hose runs, the cold water streams over chest, belly and legs, a fan from the garage provides wind. After a few minutes the dog lifts his head, the tongue draws back a little. The thermometer falls. The owner loads him into the car: door open, dog in, windows down, off at once — only the drive pulls the trapped heat out of the overheated car, every minute counts. She turns the air conditioning up full and closes the windows once the cold air arrives. Cooling continues, all the way to the clinic.

Cold water instead of lukewarm — the turn that saves lives

Here it is worth looking into the research, because of all things it was cold water where the teaching was long stood on its head. For decades, guides and textbooks said: cool an overheated dog slowly and with lukewarm water, never cold — that would trigger shock. This warning had a real kernel: an older laboratory study observed that individual dogs died immediately on immersion in ice-cold water, presumably from a sudden constriction of the blood vessels that let the circulation collapse.⁶ From this single finding a blanket rule was made. Yet the same study actually argued for cool water: as early as 1980, Magazanik and colleagues showed that cool tap water (15–16 °C) cools just as fast as ice water — and, unlike ice water, triggers no shivering; above 18 °C the cooling rate dropped markedly.⁸ “Lukewarm and slow” was therefore never well founded.

The turnaround came from human medicine. In 2007 Douglas Casa and colleagues from the University of Connecticut summarised the evidence: for exertional heatstroke, cold-water immersion is the gold standard — it is “quite difficult, if not impossible, to kill an otherwise healthy athlete … if rapid cooling via cold/ice water immersion is implemented within a few minutes”.⁹⁶ And the feared shock? In the modern, controlled cooling studies it did not occur: with cold-water immersion no side effects such as hypothermia or circulatory collapse were observed.¹⁰ The historic deaths involved immersion in ice-cold water and stem from an early laboratory observation; today’s recommendation rests on the newer, controlled evidence.⁶

In 2016 veterinary medicine followed suit: in March 2016 the Veterinary Committee on Trauma (Vet-COT) of the American College of Veterinary Emergency and Critical Care (ACVECC) recommended “cool first, transport second” — cool first, then drive.⁶ And the latest research confirms it experimentally: in 2023, in a randomised study (Parnes and colleagues), the immersion bath cooled overheated working dogs significantly faster than the alternatives — with no side effects.¹⁰

The evidence over time

The remarkable thing: the evidence for cold water is not new — the old caution was poorly founded from the start. A look at the dates:

• 1980 — Magazanik et al. (Aviat Space Environ Med): tap water (15–16 °C) cools as fast as ice water, without shivering.⁸
• 2007 — Casa et al. (Exerc Sport Sci Rev): cold-water immersion as the gold standard in human medicine.⁹
• 2016 — Vet-COT / ACVECC: first veterinary guideline “cool first, transport second”.⁶
• 2020 — Hall et al. (Scientific Reports): 905,543 dogs, 14.18 % lethality, clear risk factors.⁵
• 2021 — Hall et al. (Scientific Reports): grading scheme; a single temperature is no good as a sole criterion.³
• 2022 — Hall et al. (Veterinary Sciences): higher mortality in old and short-nosed dogs; dogs locked in cars more severely affected than under physical exertion.¹¹
• 2023 — Hall et al. (Vet Sci) & Parnes et al. (Animals): only 21.7 % are cooled before transport; the immersion bath cools fastest — “tepid, slow” cooling remains without evidence.⁶¹⁰

Why then does the outdated teaching persist even in the leaflets of respected universities? Because the path from study to guide is long: research becomes guidelines, then textbooks, finally owner brochures — that takes years. A leaflet once printed is rarely revised. The specialist literature names this persistence explicitly: “tepid, slow” cooling continues to be promoted — despite overwhelming evidence to the contrary.⁶ Anyone who cools should follow the current state of research, not the age of a leaflet.

Drinking

Drinking hydrates but barely cools the body — that is the job of cooling from outside. Offer cool, fresh water. Important: do not let an overheated dog gulp down large amounts hastily all at once — the risk factor is the pace, not the temperature. That ice water triggers a gastric torsion is disproven in veterinary medicine; ice cubes can even slow the drinking pace.¹² Do not pour water into an unconscious or unresponsive dog (risk of aspiration) — only the responsive dog.²

Top heat dangers for dogs

• The closed car — the deadliest trap. At just 20 °C outside, the interior reaches 46 °C after one hour.² Dogs locked in a vehicle have more severe courses than under exertion — they cannot escape the heat.¹¹ The same applies to conservatories, caravans and garden houses: at 22 °C outside they quickly reach 47 °C.¹³ Never leave the dog in them; if a dog is locked in with symptoms, call the police.²
• Exertion in the heat. Not only sun but movement too drives up the core temperature — put walks and play in the cool edges of the day.²
• Hot ground. Asphalt and stone slabs heat up far beyond air temperature (up to ~82 °C in extremes). Rule of thumb: if you cannot keep the back of your hand on the ground for five seconds, it is too hot for the paws.¹³
• Sunburn. Dogs with light, thin or clipped coats can get a sunburn — keep to the shade, protect sensitive spots (nose, ears).¹³
• Water is not automatically a cool-down. Not every dog can swim; only let him into the water if he can safely handle it.¹³
• Short-nosed, overweight, old or pre-diseased dogs are especially at risk and need protection sooner.⁵¹¹

Preparing before it counts

The owner in our story had a decisive advantage: she was prepared. Two things can be done today, calmly.

First, download the first-aid brochure of the University of Veterinary Medicine Hannover (TiHo) and save it on your smartphone and PC, so it is instantly there even without internet: First aid for your dog (PDF, TiHo Hannover) . The brochure is excellent for all of first aid (poisoning, gastric torsion, resuscitation) — only for cooling does the newer state apply, the one this article backs with sources (cold water, fast), not the “lukewarm and slow” named there.

Second, fill in the emergency card, print it and keep it within reach — ideally twice (the A4 template provides two cards): one on the fridge door with the other emergency numbers, and one in the car. It contains the first-aid steps and fields for your clinic’s numbers:

🖨️ Emergency card as a printable PDF: A4 – 2 cards to cut out

You can find the right emergency service through your own vet (whose answering machine usually names the current on-call practice), through the emergency-service directory of your state’s veterinary association, or through a search for “veterinary emergency service” with your location. Important: call before setting off, so the clinic can prepare the emergency admission.

How it turned out

At the clinic, thanks to the early cooling, the body temperature is already almost back in the normal range. The vet checks circulation and organ values, hooks up an infusion, keeps the dog for a few hours of observation — because even after visible recovery, organ damage can appear with a delay.¹ In the evening he is allowed home. He came through it, and for one single reason: his owner recognised it early, cooled it correctly and was prepared.

That is the whole story — and at the same time the whole lesson. Heatstroke is more often fatal than most people believe, and hits short-nosed, overweight, old or pre-diseased dogs especially hard. It is recognisable by panting, altered gums, staggering, vomiting and seizures — not by a single number on the thermometer. And the most important thing, which the fewest get right: cold water, fast — cool first, drive second. Anyone who knows this and has the emergency card filled in and lying in the car has, at the decisive moment, the head start that saves a life.