Heatstroke in dogs: symptoms, first aid and prevention

Overview

Heatstroke is a severe form of heat-related illness involving dysfunction of the central nervous system. Milder overheating may initially appear as tiredness and altered breathing. The condition can progress rapidly to organ damage and death.

A dog's normal body temperature is about 38–39 °C. Heatstroke often involves a temperature above 41 °C together with neurological signs. However, do not wait for a thermometer to reach that reading before starting first aid.

A normal or low temperature measured at the practice does not rule out heatstroke. Your dog may already have cooled down before examination, even though tissue damage has occurred.

Cases have been described in every season, although most occur in summer. In summer, ordinary activities in the garden and on walks can also carry a risk.

Causes

Too much heat can build up either because production increases or because heat loss becomes less effective. Running and other muscular activity produce heat. Exercise-related heat illness can develop even in moderate or cool weather.

Of the heat-related illness events recorded at British veterinary practices in 2016, 74.2% were associated with exertion. Simply avoiding leaving a dog in a hot car therefore does not remove every dangerous situation.

Dogs cool themselves mainly by panting, which allows water to evaporate from the airways. High humidity makes heat loss more difficult. Poor ventilation and confinement in an enclosed space also increase the heat burden.

A hot car, garage or another poorly ventilated space can cause overheating even at rest. Narrowed airways can impair your dog's own cooling mechanism.

The average WBGT heat index in the British exertional cases was 16.5 °C. This index accounts for radiation, humidity and wind as well as air temperature. It is not the same as the reading on an ordinary outdoor thermometer.

Risk factors

Any dog can develop heatstroke, including a healthy, fit dog. Short-nosed dogs cannot cool themselves by panting as effectively as other dogs. Examples include Pugs, English Bulldogs and Boston Terriers.

Excess weight increases the risk of illness. Heart and respiratory disease can also reduce heat tolerance. A thick coat and dark coat colour are further risk factors.

Age-related risk depends on the circumstances: in a British study, dogs younger than 2 years had the highest risk of exertional heat-related illness. Dogs older than 12 years had a higher risk from environmental heat than those younger than 2 years. Dogs weighing less than 10 kilograms had a lower risk of illness than heavier dogs.

The first warm days of spring can be dangerous before your dog has acclimatised to heat. Dehydration makes heat loss even less effective.

Typical symptoms

The first signs can resemble ordinary tiredness, so continuing exercise when signs are present is dangerous. Look particularly for these changes:

• Panting that is heavier than usual or continuous.
• Seeking shade and reluctance to continue playing or moving.
• Unusually lying down during exercise.
• Restlessness or an anxious expression.
• Excessive drooling or foaming at the mouth.
• Gums that are brighter red than usual or very pale.
• Vomiting or diarrhoea, which may become bloody.
• Trembling, unsteadiness or weakness in the limbs.
• Confusion, seizures or loss of consciousness.

Severity is assessed from the history of events, body temperature and your dog's other signs. Severe heat-related illness can involve bleeding disorders and liver or kidney damage.

Complications and consequences

Heat can damage cells directly and trigger an inflammatory response throughout the body. This can lead to dysfunction of several organs at the same time.

Circulation can become impaired as blood vessels widen markedly. Evaporation, vomiting and diarrhoea increase fluid loss. Intestinal damage can cause ulcers and bleeding in the lining.

The clotting system may become activated and use up platelets and clotting factors. This can lead to a widespread clotting disorder called disseminated intravascular coagulation, or DIC. Acute kidney injury is also possible.

In a hospital study of 42 patients published in 2024, mortality was 31%. That figure applies to those heatstroke patients, rather than every dog panting in hot weather. In British studies, severe heat-related illness carried 65 times the risk of death compared with mild illness. The outlook is much better for a mild case that is cooled and treated promptly.

Alongside heat, poor circulation and muscle cell breakdown can contribute to kidney damage. Bacteria can enter the body from the damaged intestine, particularly when its lining is bleeding. Heat and clotting disorders can also cause bleeding into the lungs.

Diagnosis at the vet

The vet asks about the circumstances in which signs began and whether your dog was cooled before arrival. Body temperature is assessed together with breathing, circulation and level of consciousness. The temperature recorded at the practice alone does not show the severity of damage.

Noisy breathing may suggest upper airway narrowing, swelling or a problem with the larynx. A dog that has vomited and is poorly responsive is also assessed for inhalation of vomit into the airways.

Blood samples are checked for findings including blood cell counts and blood glucose. A blood smear helps confirm the platelet count. Clotting tests can detect delayed clotting and depletion of clotting factors.

Clotting problems may worsen later: in the study of 42 dogs, most had normal clotting on arrival. Just 12–24 hours later, about 63% had impaired clotting on the tests used. This supports repeating tests beyond the initial assessment.

Kidney health is monitored through urine samples and kidney blood values. Urine output helps assess kidney function during treatment. Blood and urine tests may need to be repeated in severe heatstroke.

Low blood glucose can result from increased consumption or severe infection. Pinpoint skin haemorrhages can arise directly from heat damage to capillaries. They do not therefore automatically indicate a widespread clotting disorder.

Treatment

The vet prescribes medicines and supportive treatment according to your dog's condition. First aid at home involves effective cooling, which continues at the practice if needed.

Run cool water over the body from behind the neck, particularly over the sparsely haired abdomen. Water needs to reach the skin, even through a thick coat. Moving air, such as from a fan, makes cooling with water more effective.

Do not direct water at the muzzle or mouth, to avoid your dog inhaling it. Cooling only the paws is not recommended as a way to cool the whole dog. Do not cover your dog with a wet towel. A continuous flow of water over the body is more effective than a single soaking.

If rectal temperature can be measured safely and breathing is not rasping or wheezing, stop active cooling at about 39.7–40 °C. With rasping or wheezing from upper airway obstruction, continue cooling until panting clearly eases or the temperature reaches 38.6 °C, whichever happens first. These are limits for stopping cooling, not thresholds for seeking treatment.

If temperature cannot be measured, cool your dog for about 15 minutes before transport. Then pat your dog dry and take them to the practice immediately. Cooling must be carried out safely without endangering the person helping.

At the practice, intravenous fluids support circulation and help with cooling. Supplemental oxygen may ease the work of breathing. Severe airway obstruction may require a breathing tube and assisted ventilation. Seizures and other serious signs are treated with medicines as needed.

A clotting disorder with bleeding may require plasma or other blood products. Dialysis may be needed for severe kidney injury. Antibiotics are not automatically needed for every heatstroke patient. Several days of hospital treatment may be necessary.

If fluids do not restore circulation adequately, medicines supporting blood pressure and the heart's pumping action may be needed. Adequate nutrition is provided through a feeding tube if necessary.

Prevention

• Schedule walks for the cool morning or evening rather than the heat of midday.
• Reduce exertion in hot, humid weather, particularly in early summer before acclimatisation.
• Keep shade and fresh drinking water available at all times.
• Take a water bottle and bowl on walks, and stop for drinking breaks.
• Do not leave your dog in a car in warm weather, even in shade with the windows slightly open.
• During car journeys, make sure cool air also reaches the travel crate and luggage compartment.
• Keep your dog at a healthy weight, as excess fat makes cooling more difficult.

A car parked in shade can heat up quickly even with the windows open. Do not tie your dog in a spot in the garden where they will be exposed to direct sun. On very hot or humid days, a cool indoor space may be safer than being outdoors.

A harness can reduce pressure on the neck and make panting easier, particularly for dogs with breathing problems. Heating inside a car can be fastest within the first 15–30 minutes.

Important for dog owners

For summer outings, take water, a drinking bowl and details of the nearest open veterinary practice. Tell the emergency team when signs began, how long exertion or heat exposure lasted and what first aid you provided. This information adds to the assessment made at the practice.

You can offer water to a conscious dog, but do not force them to drink. Use air conditioning or safely opened windows during transport. Avoid getting water on the muzzle during the journey too.

After discharge, monitor your dog particularly carefully for the next 24–48 hours. New vomiting, diarrhoea, confusion or reduced appetite means you should contact the vet treating your dog. A follow-up appointment is often needed a few days after discharge.

Frequently asked questions

Can a dog get heatstroke on an ordinary walk?

Yes, heat-related illness can develop during walking, play or other everyday exercise. It does not require being left in a hot car, or even always require very hot weather. A short nose and narrowed airways can impair heat loss more than usual.

Should I cool my dog first or go straight to the vet?

Start effective cooling at the scene before transport if this can be done safely. This prevents heat damage from continuing throughout the car journey. After cooling, take your dog straight to a vet for further examination and monitoring of vital functions.

Can I wrap my dog in a wet towel?

Do not cover your dog with a wet towel, as covering can increase overheating. Cool water running over the body reaches the skin more effectively and is replaced as it warms. Wetting only the paws does not replace cooling your dog's body. Airflow makes cooling more effective alongside water.

Does a normal temperature rule out heatstroke?

No, because a dog may cool down before reaching the vet even though organ damage has already occurred. Severity is assessed from the combined history, signs and investigation results. A temperature reading that appears to have returned to normal therefore does not, on its own, determine the need for further care.

Does my dog need a vet if cooling makes them brighter?

Suspected heatstroke needs veterinary assessment even after cooling. A clotting disorder, for example, can develop after the first examination. Severe disease also carries a risk of damage to the kidneys and other organs. Further tests assess whether your dog needs hospital monitoring or other supportive care.