Dog Heatstroke Symptoms: Early Warning Signs You Should Never Ignore

Heatstroke in dogs does not always begin with collapse. Early warning signs can include unusually heavy or persistent panting, changes in breathing, tiredness, reluctance to exercise, restlessness, excessive drooling and changes to the colour of the gums or tongue. As heat-related illness becomes more severe, a dog may vomit, develop diarrhoea, become weak or uncoordinated, collapse, have seizures or lose consciousness.

If you think your dog may be overheating, do not wait for severe symptoms to appear.

A single symptom cannot confirm that a dog has heatstroke. Panting, tiredness, vomiting and other signs can have many causes. What matters is the combination of symptoms, the circumstances in which they developed and whether the dog’s condition is worsening.

What Are the Early Signs of Heatstroke in Dogs?

The earliest signs can be surprisingly easy to dismiss, particularly if a dog has just been walking, playing or exercising.

Watch for changes such as:

• unusually heavy or persistent panting;
• altered, noisy or increasingly difficult breathing;
• unusual tiredness or reluctance to continue exercising;
• restlessness or agitation;
• excessive drooling or salivation;
• seeking water or trying to find somewhere cooler;
• red or otherwise abnormal-looking gums or tongue;
• a noticeable change in normal behaviour.

Research using UK veterinary records found that respiratory changes and lethargy were the two most frequently recorded clinical signs among 856 heat-related illness events. The same research showed that heat-related illness can progress from relatively mild signs to gastrointestinal and neurological problems.

This is why recognising a change from your dog’s normal behaviour can be more useful than waiting for one dramatic “heatstroke symptom”.

Not every dog will develop the same signs or develop them in the same order.

Normal Panting or a Heatstroke Warning Sign?

Panting by itself does not mean that a dog has heatstroke. Panting is one of the main ways dogs lose excess heat.

The important question is whether the panting makes sense for the situation and whether your dog is recovering normally.

Panting becomes more concerning when it is unusually intense, continues heavily after activity has stopped, or occurs alongside other changes such as:

• noisy or difficult breathing;
• unusual lethargy;
• reluctance to walk or play;
• excessive drooling;
• weakness;
• abnormal gum or tongue colour;
• vomiting or diarrhoea;
• confusion or poor coordination.

UK VetCompass research supports this emphasis on breathing changes: altered respiration was the most frequently recorded clinical sign in dogs treated for heat-related illness in the study.

If your dog’s panting seems markedly different from normal and there is a plausible reason for overheating — such as exercise, a hot environment or being unable to escape a source of heat — stop the activity and start cooling rather than waiting to see whether more symptoms develop.

For a broader explanation of the condition, including causes, treatment and prevention, see Dog Heatstroke: Symptoms, Treatment & Prevention (Complete Guide).

How Heatstroke Symptoms Can Progress

Heat-related illness is progressive, but that does not mean every dog will move through a predictable sequence of symptoms.

A useful way to think about the signs is by increasing concern:

Earlier warning signs	Increasing concern	Severe/emergency signs
Heavy or persistent panting	Excessive drooling	Marked confusion or disorientation
Changes in breathing	Vomiting or diarrhoea	Serious loss of coordination
Unusual tiredness	Weakness	Multiple seizures
Reluctance to exercise	Increasing breathing difficulty	Loss of consciousness
Behavioural change or restlessness	Collapse	Blood in vomit or diarrhoea
Abnormal gum or tongue colour	A seizure	Severe neurological deterioration

Do not use this table as a checklist that must progress from left to right. A dog does not need to display every earlier symptom before developing serious heat-related illness, and an apparently “mild” sign does not guarantee that the condition will remain mild.

A 2026 study evaluated and validated a revised VetCompass clinical grading tool using dogs treated at UK emergency veterinary clinics. The research supports assessing heat-related illness according to the dog’s clinical presentation and severity rather than relying on a single symptom.

Body temperature can provide useful additional information, but it should also be interpreted alongside your dog’s symptoms and circumstances. Our Dog Heatstroke Temperature Chart & Dangerous Body Temperatures explains what normal, elevated and critically high readings can mean.

What Do a Dog’s Gums and Tongue Look Like With Heatstroke?

Changes to the gums and tongue can occur with heatstroke, but colour alone cannot diagnose it.

Red gums and a red tongue are recognised signs of overheating and heatstroke. Very pale gums can also be concerning, particularly when accompanied by other symptoms such as weakness, breathing changes, collapse or altered behaviour.

The safest approach is therefore not to ask whether your dog’s gums match a particular photograph or shade of red. Look at the whole picture:

• Has your dog been exercising or exposed to heat?
• Is the panting unusually heavy?
• Has their breathing changed?
• Are they drooling excessively?
• Are they unusually tired, restless or weak?
• Are they vomiting or developing diarrhoea?
• Are they becoming unsteady, confused or less responsive?

If heatstroke is a realistic possibility, start cooling and contact a vet rather than waiting for gum colour to change further.

Can Heatstroke Cause Vomiting and Diarrhoea?

Yes. Vomiting and diarrhoea can occur in dogs with heat-related illness.

They are particularly concerning when they develop alongside excessive panting, breathing changes, drooling, weakness, lethargy or other evidence that the dog has become overheated.

Blood in vomit or diarrhoea is a severe warning sign. Research into heat-related illness in UK dogs found gastrointestinal haemorrhage to be among the clinical signs associated with the highest relative risk of death.

A dog that is vomiting or has diarrhoea after becoming overheated should not simply be assumed to have an upset stomach.

Severe Heatstroke Symptoms: When It’s an Emergency

Heatstroke can affect multiple body systems as it becomes more severe.

Serious warning signs include:

• marked difficulty breathing;
• severe weakness;
• loss of coordination;
• confusion or disorientation;
• collapse;
• seizures, particularly repeated seizures;
• loss of consciousness;
• blood in vomit or diarrhoea;
• becoming poorly responsive or unresponsive.

These symptoms require emergency veterinary care. If heatstroke is suspected, start cooling immediately while arranging veterinary help.

However, collapse is not the point at which heatstroke becomes worth taking seriously. Earlier recognition gives you the opportunity to act before the condition reaches this stage.

The 2021 VetCompass study found that neurological dysfunction, gastrointestinal haemorrhage and bleeding disorders carried the highest relative risks of death among the clinical signs examined. More recent 2026 research has further validated a clinical grading approach for assessing the severity of canine heat-related illness.

What Should I Do If I Think My Dog Has Heatstroke?

Act immediately.

1. Stop further heating

Stop exercise and move your dog out of direct sun, a hot vehicle, hot building or other source of heat.

Get them into shade or a cooler, well-ventilated area.

2. Start cooling

Current UK guidance supports using water that is cooler than the dog’s body to begin cooling immediately.

The RSPCA advises pouring available water that is cooler than the dog over the body while avoiding the head, and creating a breeze by fanning the dog. PDSA advises that cold tap water can be used, while taking care to keep water away from the nose and mouth.

Do not wrap your dog in a wet towel. Covering the body can trap heat rather than allowing it to escape.

Do not force your dog to drink.

3. Contact a vet

Call your vet as soon as possible. If someone else is with you, they can make the call while cooling begins.

Tell the veterinary practice:

• what happened;
• how long your dog may have been exposed to heat or exercising;
• the symptoms you have noticed;
• what cooling you have already started;
• whether your dog’s condition is changing.

Follow the veterinary team’s instructions and transport your dog in a cool, well-ventilated vehicle, continuing appropriate cooling where practical.

For a clear step-by-step emergency sequence, Dog Heatstroke First Aid: What to Do in an Emergency explains what to do from the moment overheating is suspected through to veterinary care.

Can a Dog Seem Better and Still Need a Vet?

Yes. An improvement after cooling should not be used on its own to decide that veterinary help is unnecessary.

Heat-related illness can cause problems that are not obvious simply from looking at the dog, and a dog appearing cooler or more alert does not establish that there are no complications.

If you have genuinely suspected heatstroke, contact a vet and explain what happened even if your dog appears to improve after cooling.

This is particularly important after significant heat exposure or where the dog has experienced vomiting, diarrhoea, weakness, collapse, neurological changes or abnormal breathing.

Avoid trying to decide that your dog is “safe” based on a fixed period of apparent recovery. There is no simple waiting time that reliably rules out heat-related illness.

Which Dogs Need Extra Vigilance?

Any dog can develop heat-related illness, but risk is not equal for every dog.

Factors associated with increased vulnerability or poorer outcomes include age, bodyweight, skull shape and the circumstances that caused the heat exposure. UK VetCompass research found that older dogs and brachycephalic — flat-faced — dogs affected by heat-related illness had a greater risk of a fatal outcome.

Extra care is sensible with:

• flat-faced breeds;
• older dogs;
• overweight dogs;
• dogs with breathing or relevant health problems;
• dogs exercising intensely;
• dogs unable to move away from a source of heat.

If your dog is particularly vulnerable — or you simply want to reduce the risk before problems develop — our guide to preventing dog heatstroke explains the practical precautions you can take during exercise, at home and when travelling.

For a fuller look at how breed, body shape and other characteristics affect vulnerability, see Dog Breeds Most at Risk of Heatstroke.

Remember that heatstroke is not restricted to dogs outside in strong sunshine. Hot, poorly ventilated indoor environments can also create dangerous conditions. Can Dogs Get Heatstroke Indoors? explains how indoor overheating can happen and the situations in which owners need to be particularly careful.

Don’t Wait for Your Dog to Collapse

The most important heatstroke symptoms are not necessarily the most dramatic ones.

Unusually heavy panting, altered breathing, unexpected lethargy or a noticeable change in behaviour may provide an earlier warning that something is wrong. Drooling, vomiting, diarrhoea, weakness, poor coordination, confusion, collapse, seizures or loss of consciousness indicate increasing concern.

If you think your dog is overheating, stop the heat exposure, start cooling and contact a vet. Do not wait for collapse before acting.