Overheating (hyperthermia)

Author: Dr. med. vet. Gisa Löwe | Last modified: 17.02.2026
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Danger of overheating if the dog is left in the car during the warm season.

Heatstroke (overheating)
Heatstroke is an acute overheating of the body with failure of temperature regulation, usually due to high ambient temperature, exercise or lack of cooling. It leads to circulatory disorders, neurological symptoms and organ damage. The condition is life-threatening and requires immediate treatment.

Hyperthermia refers to a condition in which an animal’s body temperature rises above the physiological normal range. In dogs and cats, normal body temperature is between 38.0 and 39.0 °C. In veterinary medicine, hyperthermia is defined as a rectal temperature above 39.5 °C. In contrast to Fever, in which the body actively increases the target temperature (e.g. as a reaction to infections), hyperthermia is a passive overheating in which the body’s own cooling mechanisms are overwhelmed.

Dogs and cats have limited options for thermoregulation. Unlike humans, they have hardly any sweat glands distributed over their bodies. Dogs mainly regulate their body temperature by Panting, whereby heat is released via the moist mucous membranes of the respiratory tract. In addition to Panting, cats also use licking their fur to cool down through evaporation. In both animal species, extreme heat exposure or physical exertion can quickly overwhelm these cooling mechanisms, leading to a dangerous Increase in body temperature.

Causes

There are many causes of hyperthermia in dogs and cats. The most common form is classic Heatstroke, which is triggered by high ambient temperatures. Closed spaces such as cars, which can heat up to over 60 °C in the sun within a few minutes, are particularly dangerous. Prolonged stays in direct sunlight without shade can also lead to overheating.

Another common cause is hyperthermia caused by intense physical activity in warm weather. This mainly affects dogs that play, run or are trained too intensely in the heat. Stress can also contribute to an Increased body temperature, as it increases the metabolic rate.

Certain groups of animals are particularly at risk. These include brachycephalic (short-headed) breeds such as pugs, bulldogs, boxers or Persian cats, whose shortened airways make it difficult to release heat through Panting. Overweight animals, puppies and seniors, as well as animals with pre-existing conditions (especially heart and respiratory diseases) also have an increased risk. Long-haired breeds and animals with dark fur also absorb more solar heat and overheat more quickly.

Symptoms

Overheating (hyperthermia/Heatstroke) in dogs and cats

Typical Symptoms:

  • Severe Panting, Restlessness, drooling
  • Vomiting, Diarrhea, weakness,
  • Reddened mucous membranes, Increased body temperature
  • Drowsiness, wobbly gait, Staggering / ataxia

Alarm signs:

  • Lying on their side
  • Weak, rapid pulse
  • Collapse, Seizures, altered consciousness
  • Bleeding/petechiae, black feces (DIC possible)
  • Shortness of breath, cyanosis, very high temperature + “dry” Panting
  • Vomiting/diarrhea + extreme apathy

Escalation/course:

  • Minutes: neurological symptoms → critical
  • Hours: organ failure/DIC can occur with a delay, even after cooling
  • Later deterioration within 4–24 h → intensive care required

 

The symptoms of hyperthermia develop progressively and can vary depending on the severity. In the early stages, affected animals show increased Panting, increased respiratory rate, increased heartbeat and restless behavior. The mucous membranes appear intensely red and salivation increases. Many animals actively seek out cooler places or lie down on cool surfaces.

As overheating progresses, weakness, Drowsiness, and Coordination disorders occur. The animals may Staggering / ataxia or show an unsteady gait. Vomiting and Diarrhea are common accompanying symptoms. The respiratory rate continues to increase, while the depth of breathing decreases – the Panting becomes more superficial and ineffective.

In severe cases, neurological symptoms such as muscle tremors, Seizures or even unconsciousness occur. The pulse becomes weak and rapid, and the mucous membranes may turn bluish due to lack of oxygen. Without immediate treatment, organ failure, coagulation disorders (DIC), cerebral edema and finally Death threaten. At body temperatures above 43 °C, the Prognosis is extremely unfavorable, as irreversible cell damage occurs in vital organs.

First Aid

  1. Take your pet to a shady, cool place.
  2. Remove the collar.
  3. Wet the animal’s abdomen (few hairs) with water or place wet towels on the animal.
  4. If you are at home and have enough water available, soak your entire animal down to the skin.
  5. Offer it water that is not too cold, but do not force it to drink anything.

When should you see a vet sooner?

→ Red if there is collapse, seizures, Bleeding, altered consciousness, or a very high temperature.

If your animal is unconscious or its breathing does not calm down, or if its body temperature is around 40 degrees Celsius or is rising in this range, immediately take your animal to a veterinarian.
There is a risk of “Heatstroke”, which leads to damage to the brain and other organs and is life-threatening.
If possible, continue to cool your animal with wet towels until you arrive at the veterinarian.

Diagnosis

The diagnosis of hyperthermia is made primarily by measuring body temperature in conjunction with the clinical examination and the medical history. A rectal temperature measurement is the gold standard. It is important to distinguish between hyperthermia and Fever, as the treatment approaches are different. With hyperthermia, the focus is on cooling, while with Fever, the primary focus is on combating the causes.

In veterinary practice, additional diagnostic procedures are used to assess the extent of organ damage. Blood tests provide information about electrolyte shifts, kidney and liver function, and the acid-base balance. A complete blood count can provide indications of Inflammatory conditions or coagulation disorders. The determination of lactate in the blood serves as a marker for tissue perfusion and the severity of the shock condition.

In severe cases, imaging techniques such as ultrasound can be used to identify organ damage. An ECG helps to detect heat-related Cardiac arrhythmia. In specialized facilities, extended neurological examinations can also be carried out to assess brain damage.

Further veterinary measures

In the small animal practice/Klinik, your animal can be shaved and further cooling can be promoted.
Secondary damage such as cerebral edema, derangement of the water, electrolyte and acid-base balance or hypoglycemia can be detected and treated by laboratory diagnostic tests.

Supplement

The therapy for hyperthermia requires quick action and follows a multi-stage approach. Initial care aims to control the lowering of body temperature. This should be done gradually to avoid a too rapid drop in temperature, which can itself be dangerous.

As an immediate measure, the animal is taken to a cool, shady place and moistened with lukewarm (not ice-cold) water, especially in sparsely haired areas such as the abdomen, armpits and groin, where large blood vessels run close to the skin surface. Damp cloths can be placed on and changed regularly. Fans support evaporative cooling. The temperature should be monitored continuously, and cooling should be stopped when about 39.5 °C is reached to avoid hypothermia.

In veterinary practice or Klinik, the therapy is intensified. Intravenous fluid administration compensates for Dehydration and supports circulatory function. Oxygen is administered if necessary. Drug treatments may include anticonvulsants for Seizures, mannitol for cerebral edema, and coagulation factors for blood coagulation disorders. In severe cases, intensive care monitoring with continuous ECG monitoring and blood pressure measurement may be necessary.

Prognosis and aftercare

The Prognosis for hyperthermia depends largely on the level of body temperature reached, the duration of overheating and the speed of treatment initiated. With early intervention and moderate overheating, the Prognosis is usually good. In severe cases with temperatures above 42 °C and organ damage that has already occurred, the Prognosis can be unfavorable despite intensive treatment.

Aftercare plays a crucial role in complete recovery. In the first 24–48 hours after Heatstroke, there is an increased risk of complications such as acute renal failure, liver damage or coagulation disorders. Regular follow-up examinations with blood tests are therefore important in order to detect and treat organ damage early.

In the long term, animals that have survived severe Heatstroke may develop increased sensitivity to heat. Owners should therefore be particularly careful and consistently implement preventive measures. Some animals may also have neurological residues that require longer-term therapy.

Summary

Hyperthermia in dogs and cats is a potentially life-threatening emergency that requires quick action. The main causes are high ambient temperatures and excessive physical exertion in the heat. Brachycephalic breeds, Overweight animals, very young or old animals and animals with pre-existing conditions are particularly at risk.

The symptoms develop progressively, from increased Panting to Coordination disorders to unconsciousness and organ failure. The diagnosis is made by measuring the temperature and clinical examination, supplemented by laboratory diagnostic procedures to assess organ damage.

The therapy includes controlled lowering of body temperature, fluid therapy and treatment of complications. The Prognosis is usually good with early intervention, but can be unfavorable in severe cases with organ failure. Preventive measures such as avoiding exertion in the heat and never leaving animals in the car are crucial to prevent hyperthermia.

Outlook on current research

Research in the field of hyperthermia in small animals is currently focused on several key areas. New biomarkers are being investigated that should enable earlier detection of organ damage. Studies on specific laboratory parameters such as heat shock proteins could allow a more precise Prognosis in the future.

Another area of ​​research concerns innovative cooling methods. Experimental approaches such as selective brain cooling or special cooling infusions are showing promising results in initial studies. The development of drugs that specifically interrupt the cascade of Inflammatory conditions triggered by heat is also the focus of current investigations.

Genetic studies in brachycephalic breeds could lead to breeding recommendations in the long term that reduce the risk of heat-related problems. At the same time, improved prevention strategies are being developed, including wearables for temperature monitoring and early warning systems for pet owners.

Frequently asked questions (FAQs)

  1. From what temperature is there a dangerous hyperthermia in dogs and cats?
    There is an acute danger from a body temperature of around 41 °C. Temperatures above 42 °C can already lead to irreversible organ damage.
  2. How long does it take for an animal to overheat in a closed car?
    At outside temperatures of 20 °C or more, a car in the sun can heat up to dangerous temperatures within 10–30 minutes, even with the windows slightly open.
  3. Which dog breeds are particularly susceptible to overheating?
    Brachycephalic (short-headed) breeds such as pugs, bulldogs, boxers, Pekingese, as well as long-haired breeds and dogs with dark fur are particularly at risk.
  4. Can I give my overheated animal ice cubes or very cold water?
    No, water that is too cold can trigger shock and constrict the blood vessels, which impairs heat release. Use lukewarm to cool water instead.
  5. How do I know if my animal has Heatstroke or is just exhausted?
    Extreme exhaustion can be an early sign of Heatstroke. Watch out for severe Panting, Staggering / ataxia gait, glassy eyes, dark red tongue and Drowsiness as warning signs.
  6. Can an animal suffer long-term damage after surviving Heatstroke?
    Yes, possible long-term consequences include kidney and liver damage, neurological problems and increased sensitivity to heat in the future.
  7. What is the best way to cool my animal on hot days?
    Offer cool, shady resting places, provide several water bowls, use damp towels as a base and plan walks in the early morning or late evening hours.
  8. Is it dangerous if my dog ​​is shivering after swimming in cold water?
    Slight shivering after swimming is normal and a sign that the body is trying to produce heat. However, make sure that hypothermia does not occur.
  9. Can cats also suffer from Heatstroke?
    Yes, although cats can often cope with heat better than dogs, they are also at risk, especially if they are trapped in overheated rooms or if they are brachycephalic breeds such as Persian cats.
  10. How do I prepare my animal for hot summer days?
    Gradually get your animal used to rising temperatures, ensure adequate hydration, avoid Overweight and adapt activities to the temperatures.

Literature

  • Bruchim Y, Klement E, Saragusty J, Finkeilstein E, Kass P, Aroch I.: Heat stroke in dogs: A retrospective study of 54 cases (1999-2004) and analysis of risk factors for death. J Vet Intern Med. 2006 Jan-Feb;20(1):38-46.
  • Jenny McIntosh: Heatstroke – a seasonal challenge. In: kleintier konkret. Volume 20, Issue 2, 2017, pp. 23–31.
  • Löwe, G. and Löwe, O. (2021). Emergencies in dogs and cats – A veterinary Guide. Kynos-Verlag. 208 pp.
  • Bruchim Y, Segev G, Kelmer E, et al. Hospitalized dogs recovery from naturally occurring heatstroke; does serum heat shock protein 72 can provide prognostic biomarker? Cell Stress Chaperones. 2020;25(3):455-464.
  • Hall EJ, Carter AJ, O’Neill DG. Dogs Don’t Die Just in Hot Cars—Exertional Heat-Related Illness (Heatstroke) Is a Greater Threat to UK Dogs. Animals. 2020;10(8):1324.
  • Hemmelgarn C, Gannon K. Heatstroke: Clinical Signs, Diagnosis, Treatment, and Prognosis. Compendium on Continuing Education for the Practicing Veterinarian. 2021;35(7):E3.
  • Johnson SI, McMichael M, White G. Heatstroke in small animal medicine: a clinical practice review. Journal of Veterinary Emergency and Critical Care. 2019;29(1):9-22.
  • Teichmann S, Türk J, Dörfelt R. Hyperthermie, Hitzschlag und maligne Hyperthermie bei Hund und Katze. Veterinary Practice Small Animals. 2022;42(1):13-20.