Most pet owners know that leaving a dog or cat in a parked vehicle is dangerous. What many don’t realize is that heatstroke is far more than simply becoming overheated.
From an emergency medicine perspective, heatstroke is a complex, multisystem disease that can rapidly affect the brain, kidneys, gastrointestinal tract, cardiovascular system, clotting system, and other vital organs. By the time many pets begin showing obvious signs of distress, the disease process may already be underway.
Every summer, veterinary emergency teams treat dogs and cats suffering from heat-related illness after being left in vehicles. Some patients recover with prompt intervention. Others develop life-threatening complications requiring hospitalization and intensive medical care.
For pet owners across northwest Washington, understanding what heatstroke does inside the body—and why parked vehicles remain one of its most common causes—can help prevent a completely avoidable emergency.
At Boundary Bay Veterinary Specialty Hospital in Bellingham, heatstroke is treated as a true medical emergency. Understanding how it develops helps explain why no pet should ever be left unattended in a vehicle.
Why Emergency Veterinarians Worry About Heatstroke
Heatstroke is not simply a matter of body temperature becoming too high. Elevated body temperatures can trigger widespread inflammation and cellular injury throughout the body.
As temperatures rise, proteins and cellular structures begin to malfunction. Blood flow may become impaired, inflammation can intensify, and multiple organ systems may be affected simultaneously.
Potential complications include:
- Gastrointestinal injury and damage to the intestinal barrier
- Abnormal blood clotting and bleeding disorders
- Kidney injury
- Cardiovascular instability
- Neurologic dysfunction, including seizures or altered consciousness
- Respiratory compromise
- Shock
- Multiple-organ dysfunction
The longer elevated temperatures persist, the greater the risk of severe complications. This is why emergency veterinarians treat heatstroke aggressively—even when a patient initially appears stable.
Why Parked Vehicles Are So Dangerous
One of the most common misconceptions is that a quick errand, a partially open window, or a mild summer day makes a parked vehicle safe. Unfortunately, that is not how heat accumulation works.
Vehicle interiors function much like greenhouses, trapping heat and limiting airflow. Temperatures inside a parked car can rise rapidly, creating conditions that quickly become dangerous for pets. Dogs and cats are also less efficient at cooling themselves than humans.
Dogs rely primarily on panting to dissipate heat, while cats depend on grooming behaviours, limited sweating through their paw pads, and behavioural adaptations. Once environmental temperatures exceed the body’s ability to cool itself, heatstroke can develop quickly.
Additional factors such as humidity, direct sunlight, vehicle colour, ventilation, and underlying medical conditions may further increase risk.
Cracking windows provides little protection, and relying on a vehicle’s air conditioning system is risky if the system shuts off unexpectedly or malfunctions.
The safest approach remains simple: If your pet cannot accompany you inside, leave them at home.
Which Pets Are Most Vulnerable?
Any dog or cat can develop heatstroke under the wrong conditions.
However, emergency veterinarians often see more severe disease in:
- Brachycephalic (short-nosed) breeds
- Senior pets
- Puppies and kittens
- Overweight pets
- Pets with heart disease
- Pets with respiratory disease
- Pets with chronic medical conditions
These patients may have a reduced ability to regulate body temperature and can become critically ill more rapidly.
Recognizing the Signs of Heatstroke
One of the challenges with heatstroke is that clinical signs can progress quickly.
Owners may observe:
- Excessive panting
- Thick saliva or drooling
- Restlessness or anxiety
- Weakness
- Vomiting
- Diarrhea
- Bright red gums
- Disorientation
- Collapse
- Seizures
Cats may show more subtle signs initially, making careful observation especially important.
Any pet showing signs of overheating should be considered a medical emergency.
Why Some Heatstroke Patients Become Critically Ill Hours Later
One of the most dangerous aspects of heatstroke is that complications do not always appear immediately.
A pet may appear improved after cooling down, yet internal injury can continue developing.
Emergency veterinarians often monitor for:
- Kidney injury
- Clotting abnormalities
- Gastrointestinal damage
- Cardiovascular instability
- Neurologic complications
For this reason, veterinary evaluation is recommended even when a pet appears to recover after a heat-related event.
What Should You Do If You See a Pet in a Hot Vehicle?
If you encounter an animal inside a parked vehicle and are concerned about its welfare:
- Record the vehicle’s make, model, colour, and licence plate number.
- Ask nearby businesses to page the owner.
- Continue monitoring the animal from a safe location.
- Contact 911, local law enforcement, or animal control if the animal appears distressed.
Washington State Law and Good Samaritan Protections
Washington law prohibits leaving animals in vehicles when conditions create a risk of harm due to heat, cold, lack of ventilation, or lack of water.
Beginning July 27, 2025, Washington’s Good Samaritan law provides legal protection for citizens who enter a vehicle to rescue an animal or vulnerable person only when specific legal requirements are met, including contacting 911 and complying with all requirements outlined in the law.
If you are uncertain whether those conditions apply, contact law enforcement immediately and follow their guidance. Read more in this article in the Bellingham Herald.
First Aid for Suspected Heatstroke
If a pet has been removed from a hot environment and is showing signs of heat-related illness:
- Move the animal to a cool, shaded area.
- Begin cooling with cool or lukewarm water.
- Avoid ice baths or ice packs.
- Use fans to promote evaporative cooling.
- Offer small amounts of water if the pet is alert and able to drink.
- Seek immediate veterinary care.
Even if clinical signs appear to improve, heatstroke-related injury may continue developing internally.
How Emergency Veterinarians Treat Heatstroke
For emergency clinicians, lowering body temperature is only the first step.
Because heatstroke can affect multiple organ systems simultaneously, patients often require comprehensive diagnostics, repeated monitoring, and supportive care.
Treatment may include:
- Continuous temperature monitoring
- Advanced bloodwork to assess organ function
- Blood pressure monitoring
- Coagulation testing to evaluate clotting abnormalities
- Oxygen therapy
- Intravenous fluid therapy
- Electrolyte monitoring and correction
- Diagnostic imaging when complications are suspected
- Intensive nursing care and hospitalization
Because heatstroke can affect multiple organs at once, emergency clinicians are often monitoring several body systems simultaneously while treatment is underway.
At Boundary Bay Veterinary Specialty Hospital in Bellingham, emergency clinicians frequently collaborate with Internal Medicine, Diagnostic Imaging, Surgery, and other specialty services when managing complex heatstroke cases.
Through the shared emergency facility model with Animal Emergency Care, patients have access to comprehensive emergency evaluation and treatment 24 hours a day. Depending on the severity of illness, hospitalization may be required even after body temperature normalizes because complications can develop hours later.
Prevention Is Far Easier Than Treatment
Heatstroke caused by parked vehicles is one of the most preventable emergencies seen in veterinary medicine.
Before leaving your vehicle, ask yourself one simple question:
Can my pet safely come inside with me?
If the answer is no, the safest option is to leave them at home in a cool, comfortable environment.
Heatstroke remains a cause of preventable illness and death in pets every summer. At Boundary Bay Veterinary Specialty Hospital in Bellingham, our emergency team works in collaboration with Animal Emergency Care to provide 24/7 emergency care, and consults with our specialists in Internal Medicine, Diagnostic Imaging, Surgery, and other services to provide advanced care for critically ill patients. When it comes to hot vehicles, prevention will always be safer than treatment—and a few minutes of planning can save a life.
Frequently Asked Questions About Heatstroke in Dogs and Cats
Why is leaving a pet in a parked car so dangerous?
Parked vehicles trap heat quickly, creating temperatures that can become life-threatening for pets. Dogs and cats cannot cool themselves as efficiently as humans, making them especially vulnerable to heatstroke.
Can a dog die from being left in a hot car?
Yes. Heatstroke can rapidly become a life-threatening medical emergency. Severe cases may lead to shock, organ failure, seizures, and death.
Can cats develop heatstroke in a parked vehicle?
Yes. Cats can also develop heatstroke if left in a hot vehicle. Because cats often show more subtle signs than dogs, their illness may not be recognized until it becomes more advanced.
Why are parked cars so dangerous even on mild days?
Vehicle interiors act like greenhouses, trapping heat and limiting airflow. Temperatures inside can rise rapidly, creating dangerous conditions even when outdoor temperatures seem comfortable.
Does opening the windows make a parked car safe for pets?
No. Cracking the windows provides very little protection against rising temperatures inside a parked vehicle and should never be relied upon to prevent heatstroke.
Is it safe to leave my pet in the car with the air conditioning running?
No. Air conditioning systems can shut off unexpectedly or malfunction, allowing the vehicle to heat up quickly. If your pet cannot safely accompany you inside, the safest option is to leave them at home.
What happens inside the body during heatstroke?
Heatstroke causes widespread inflammation and cellular injury that can affect multiple organ systems. Complications may include gastrointestinal injury, abnormal blood clotting, kidney injury, cardiovascular instability, neurologic dysfunction, respiratory compromise, shock, and multiple-organ dysfunction.
Which pets are most at risk for heatstroke?
Although any dog or cat can develop heatstroke, higher-risk patients include brachycephalic (short-nosed) breeds, senior pets, puppies, kittens, overweight pets, and those with heart disease, respiratory disease, or other chronic medical conditions.
What are the signs of heatstroke in dogs?
Signs may include excessive panting, thick saliva or drooling, restlessness, weakness, vomiting, diarrhea, bright red gums, disorientation, collapse, and seizures.
What are the signs of heatstroke in cats?
Cats may develop weakness, panting, drooling, vomiting, collapse, or changes in behavior. Their signs are often more subtle than those seen in dogs.
Can heatstroke continue to worsen after my pet cools down?
Yes. A pet may appear to improve after cooling, but internal injuries involving the kidneys, clotting system, gastrointestinal tract, cardiovascular system, and nervous system may continue to develop over the following hours.
What should I do if I see a pet in a hot car?
Record the vehicle’s make, model, color, and license plate number, ask nearby businesses to page the owner, continue monitoring the animal from a safe location, and contact 911, local law enforcement, or animal control if the pet appears distressed.
What should I do if my pet shows signs of heatstroke?
Move your pet to a cool, shaded area, begin cooling with cool or lukewarm water, avoid ice baths or ice packs, use fans to promote cooling, offer small amounts of water if your pet is alert, and seek immediate veterinary care.
Should I use ice to cool my overheated pet?
No. Ice baths and ice packs are not recommended. Cooling with cool or lukewarm water while seeking immediate veterinary care is generally preferred.
How do emergency veterinarians treat heatstroke?
Treatment may include continuous temperature monitoring, bloodwork, blood pressure monitoring, clotting tests, oxygen therapy, intravenous fluids, electrolyte correction, diagnostic imaging, intensive nursing care, and hospitalization.
Why might my pet need to stay in the hospital after heatstroke?
Even after body temperature returns to normal, complications affecting multiple organs can continue to develop. Hospitalization allows veterinarians to monitor for these delayed problems and provide ongoing treatment if needed.
Can heatstroke be prevented?
Yes. Heatstroke caused by parked vehicles is one of the most preventable veterinary emergencies. If your pet cannot safely accompany you inside, the safest choice is to leave them at home in a cool, comfortable environment.
