Heat stroke should be considered in any animal that presents with a core body temperature higher than 106oF without any obvious evidence of infection. Clinical presentation can sometimes give clues to whether the animal's elevated temperature is pyrogenic or non-pyrogenic. Pyrogenic hyperthermia causes a change in the set point, a heat-dissipating mechanism observed in systemic infections. Animals that have elevated temperatures due to infections will most likely not be panting and hypersalivating. As compared to hyperthermic or heat stroke animals, the heat-dissipating mechanism is panting along with salivation. Also, pyrogenic animals will mostly be ambulatory whereas most heat stroke animals have the inability or unwillingness to rise. Mucous membranes will be darkened or hyperemic due to systemic vasodilation. The capillary refill time may be immediate and even non-detectable. Dogs may exhibit ataxia, muscle tremors, loss of consciousness, cortical blindness, seizures, or even coma. Many animals exhibit other signs of shock like vomiting and bloody diarrhea.

A thorough history is very important in determining the reason for the hyperthermic event. Careful questioning may reveal that the dog had been locked up in the car on a hot day for sometime. There are some reports of dogs experiencing hyperthermia associated by air transport shipped during the summer months. Also, there may be other pathologic diseases present that prevented proper heat-dissipation such as laryngeal paralysis, upper airway disease, neurologic disease, cardiovascular disease, or some other disease process that perpetuated the hyperthermic event. Loud breathing sounds may be detected in dogs with underlying anatomical defects of the upper airway.

Examination of the mucous membranes, pinna, and vulva may reveal petechial hemorrhages or ecchymosis indicating disseminated intravascular coagulation (Figures 1, 2, & 3). Tachycardia is usually present along with pulse deficits or thready pulses due to the extreme dehydration. Melena, bloody diarrhea, or mucosal sloughing may be detected on rectal examination.