Causes
Ambient heat, exercise during hot hours, leaving the animal in a car (FATAL within minutes), lack of shade and water. Brachycephalic breeds (Bulldog, Pug), seniors, overweight animals and rabbits are the most vulnerable.
Diagnosis
Immediate diagnosis based on the situation and clinical signs. The vet measures the temperature and assesses organ damage.
Treatment
FIRST AID while you head to the vet: move the animal to a cool area, wet it with lukewarm water (NEVER ice-cold, as it causes vasoconstriction), provide ventilation, offer water if conscious. Afterwards, ALWAYS seek veterinary care — internal damage can appear hours later.
Prevention
NEVER leave the animal in the car. Walk during cooler hours in summer. Shade and water always available. Take special care with brachycephalic breeds, seniors and rabbits.

