In the summer, think of your car as an oven. Even with the windows cracked, temperatures in a vehicle can get exceedingly hot in an extremely short period of time. As a result, just a few minutes alone in a hot car can be extremely dangerous - even fatal - for a small child or pet.
It is never OK to leave children or pets unattended in a car for any amount of time. On a 72-degree day, the temperature inside a car can increase by 30 to 40 degrees in an hour. Seventy percent of this increase occurs the first 30 minutes.
Children are at higher risk for heat-related illness and injury than adults because their bodies make more heat relative to their size and their abilities to cool through sweating are not as developed as adults.
Animals are at particular risk for heat stroke if they are very old, very young, overweight, not conditioned to prolonged exercise, or have heart or respiratory disease.
Heat stroke may occur when body temperature passes 104 degrees Fahrenheit. That overwhelms the brain's temperature control, causing symptoms like dizziness, disorientation, agitation, confusion, sluggishness, seizure, loss of consciousness or death.
Signs of heatstroke in pets, according to the Humane Society of the United States, include heavy panting, glazed eyes, rapid heartbeat, difficulty breathing, excessive thirst, lethargy, fever, lack of coordination, profuse salivation, vomiting, a deep red or purple tongue or seizure.