Heatstroke — Cool First, Vet Second

Time-Critical Thresholds

• 39.4°C / 103°F = STOP cooling (sources differ: 39.4°C / 103°F at VCA, below 40°C / 104°F at heatstroke.dog)
• 41°C / 105.8°F = heatstroke definition (the brain and nerves, the central nervous system, start to malfunction)
• 41.2–42.7°C / 106–109°F = organ failure and death can follow (VCA). How long he stays hot matters as much as the highest reading
• The sooner cooling starts, the better his chances
• Less than half of dogs with severe HRI (heat-related illness) survive (research by the RVC, the Royal Veterinary College in London)
• Only 21.7% of dogs were cooled by their owners before reaching the vet — that statistic kills French Bulldogs

Immediate Actions in Order — Wet Then Vet Protocol

1. STOP ACTIVITY. Into the nearest shade, right where you are

Carry the dog — do not let them walk. Don't delay the cooling to reach A/C or the car.

2. COOL FIRST, TRANSPORT SECOND

This is THE single most important rule. "Cool first, transport second" is the veterinary rule the RVC promotes: the longer he stays hot, the more damage is done.

3a. Cold-Water Immersion (for healthy, conscious dogs without a flat face)

• For a Frenchie, pour instead: cool or cold water over him nonstop, air moving (fan, A/C). Immersion suits young, healthy, conscious dogs without a flat face (heatstroke.dog, RVC).
• Use a bathtub or a kiddie pool, or fill a bin with a garden hose
• COLD water is correct — the old "tepid only" advice is outdated
• Submerge body, keep head above water
• Hold there continuously

3b. Evaporative Cooling (for unconscious / elderly / seizing — works on any dog)

• Pour cold water over body continuously
• Keep his fur wet the whole time — dry fur insulates
• Run a fan or A/C at full blast — air movement is critical
• DO NOT cover him with wet towels — they trap heat

4. STOP Cooling at ~39.4°C / 103°F Rectal

Measure with rectal thermometer every 5 min. Keep cooling below this temperature and he can swing into hypothermia.

5. Transport with A/C on Full

Put wet towels UNDER the dog (so air can still move over his body) and open the windows if needed.

6. Call the Vet Before You Get in the Car

Ten seconds, before you start driving. Say: "incoming heatstroke, started cooling at [time]." They need to prep IV fluids, oxygen, monitoring. If someone is with you, let them drive while you call. Alone? Call before you start — once you're moving, eyes on the road, not on the dog.

What NOT to Do — Mistakes That Kill

1. Do NOT drive off without cooling first — RVC data: most owners do, and dogs cooled before the drive have a better chance.
2. Do NOT cover him with wet towels — they hold the heat in. Pour the water straight onto his fur.
3. Do NOT force water into his mouth — he can breathe it in, and water or vomit in the lungs causes pneumonia. Never pour water into the mouth of a panting/distressed Frenchie.
4. Stopping the walk is not enough — his temperature can keep rising after he stops moving, as heat from the muscles spreads (heatstroke.dog). Keep cooling until 39.4°C / 103°F, or until he starts to shiver.
5. Do NOT keep cooling past 39.4°C (103°F) — he can get dangerously cold (hypothermia, VCA).
6. Do NOT use lukewarm water "to be safe" — it slows cooling, the dog stays in the danger zone longer
7. COLD water, not tepid — the "tepid water" advice is a debunked myth.

Cooling Methods

Body Temperature Thresholds

Temperature is only a rough guide — collapse, confusion, vomiting or pinpoint bleeding mean severe heatstroke at any temperature (VetCompass).

Why Frenchies Are a High-Risk Breed

RVC research: Chow Chows, Bulldogs, French Bulldogs (about 6.5 times the odds of a Labrador), Dogues de Bordeaux, Greyhounds, Cavaliers, Pugs, Springer Spaniels and Golden Retrievers — and dogs over 50 kg (110 lb) — had a higher risk (Hall et al. 2020).

Frenchies specifically:

• Cannot pant efficiently (panting = primary canine cooling mechanism)
• About half have BOAS (the breathing disease of flat-faced dogs) bad enough to cause problems
• Excited or stressed, a Frenchie can reach dangerous heat stress on a day a Labrador handles comfortably
• Heatstroke happens on mild days too: in UK dogs, the typical (median) air temperature on the day of heat illness was 16.9°C (62°F) (RVC, Hall et al. 2022)

Survival Depends on Cooling Speed

Multiple studies show: the faster owners start cooling and the lower the presenting temperature, the better the outcome. Specific peer-reviewed survival percentages vary widely between studies and populations.

What is consistent across all sources:

• Getting to the vet late costs lives: a delay of more than 90 minutes was linked to more deaths (Bruchim et al., 54 dogs)
• Presenting temp >43°C (109°F) carries the worst prognosis
• Owners who don't cool before transport have the worst outcomes
• Severe HRI overall: more than half of dogs (57%) die even with vet care (VetCompass, UK)

Why "Wait and See" Kills

Heatstroke builds on itself. Once his cooling system is overwhelmed, his temperature keeps climbing on its own.

Cellular damage cascades:

• Blood clotting failure (DIC)
• Kidney failure
• Gut bacteria leaking into the blood
• Brain swelling

You cannot reverse this with vet IV fluids alone — cells are already dying. What saves the dog is cooling him right away, before the drive.

Prevention

• Our opinion: 24°C (75°F) is the absolute upper limit — never walk above it, and even at 24°C (75°F) we don't recommend it. Below that, skip the walk when it is humid.
• Walk before 8am or after 8pm in summer
• Cooling vest, cooling mat, kiddie pool
• NEVER leave him in the car — at 21°C (70°F) outside, the inside reaches about 37°C (99°F) in 20 minutes and 40°C (104°F) in 30 minutes (AVMA)
• Recognize early signs: heavy panting that doesn't stop, thick rope drool, brick-red gums, stumbling, vomiting

About the Author

Spike’s Dad

Not a veterinarian — the human behind Spike, a dark brindle Frenchie, for 7+ years. What is written here is checked as carefully as we can against the sources listed above. When real life with Spike differs from the studies, we say so.

How this site is researched →