A cat basking in the sun.

Understanding Heat Stroke in Pets

Heat stroke is the most severe type of heat-related illness. Heat-related illnesses are broken down based on severity of elevated temperature and clinical signs. In humans, heat stroke has been categorized by two definitions: either a patient whose temperature is >40° C with central nervous system derangements or a hyperthermia case resulting in a severe inflammatory response that causes multi-organ dysfunction with predominant encephalopathy.

There are four categories of heat-related illnesses for veterinary patients that range from mild to severe.

These are:

There are two forms of heat stroke: exertional and non-exertional (or classic). Exertional is not commonly seen in veterinary medicine, but results from strenuous physical activity leading to hyperthermia. This is typically seen in marathon runners or other elite athletes due to strenuous exercise, often in conjunction with warm environmental temperatures. It is also common in working animals, like race horses and greyhounds, and can be caused by any form of hard exercise for animals. Classic/exertional heat stroke is caused by exposure to high environmental temperatures. This is the type of heat stroke most commonly seen and treated in veterinary medicine.

Heat Compensation Mechanisms

All animals and humans are able to compensate for some level of heat exposure through built in mechanisms, but if prolonged exposure or underlying medical conditions exist, hyperthermia can occur.

The four compensation mechanisms are:

Radiation and convection help with 70% of heat regulation in dogs and cats when environmental temperature is lower than body temperature. When ambient temperature rises, evaporation plays a larger part.

There are some predisposing conditions that can make heat stroke more likely in veterinary patients. These can be endogenous, meaning that they are outside factors, like underlying medical conditions or physical attributes, that increase the risk of developing heat stroke.

The documented endogenous and exogenous factors include:

Endogenous Factors Exogenous Factors
Obesity Lack of acclimatization to environment
Abnormal airway, common in brachycephalic breeds (such as pugs, bulldogs, and boston terriers) Water deprivation
Heart/lung disease Isolated to airway with minimal ventilation or shade (such as a dog trapped in a closed car on a hot day)
Dense hair coat Concurrent medication administration, mainly caused by heart medications, like diuretics
Muscular or neuromuscular disease

Organ Systems Involved in Heat Stroke

The common organ systems involved include the gastrointestinal tract, kidneys, neurological system, heart, lungs, and the coagulation system. The body can suffer direct cellular injury due to high temperatures, but can also suffer secondary injuries due to the hypoxia (low oxygenation) and hypovolemia (low blood pressure and dehydration).

Clinical Signs

Almost all organ systems can be affected by heat stroke, therefore clinical signs can be variable depending on the patient. Clinical signs can also be mild, even with heat stroke, and recovery can be quick or severe and life threatening.

Clinical signs can be broken down based on what organ system is dysfunctional:


Determining if a pet has heat stroke can be difficult, since observation may be hours after injury. The first step to a diagnosis is obtaining a detailed history and trying to isolate a heat injury if it occurred. A thorough physical is used to look for corresponding clinical signs and then utilizing these findings to create a treatment plan. Baseline temperature at triage may still be elevated when patients are at the veterinarian hospital, but is typically normal or decreased based on cooling measures at home or resulting from shock.

Diagnostic measures include:

Ultimately, a diagnosis is based on a patient’s history, clinical signs, and the results of diagnostic screening.

Treatment Measures

What Should I Do If My Pet Has Heat Stroke?

First of all, your pet should be removed from the source of high external temperature. Secondly, work towards getting them to a veterinary hospital immediately. During the car ride to the hospital, make the car as cool as possible with air conditioning or open windows to increase convection. Place cool towels on their body in the car and replace if they get warm. DO NOT submerge them in water, since this can increase the risk of water aspiration into the lungs. Treatment at home or on the way should not delay the arrival to the hospital, but rather be performed at the same time.

How Can I Avoid Heat Stroke In My Pets?