It's been pretty hot where I live, with temperatures in the upper 90s (Fahrenheit), and heat indexes in the low 100s. Being of Scandinavian blood, I try to avoid being outside at all in this kind of heat, as I quickly feel the effects. Any yard work is done first thing in the morning before the day has a chance to heat up much. I also make sure to drink plenty of water and take breaks.
It's in weather like this that veterinarians start to see cases of heat stress or stroke, especially in dogs. In most cases the pet was left outside in the heat without shade or an ability to get out of direct sunlight. Access to fresh water is vitally important, but it's the direct, unrelenting sunlight that causes the most harm. If a pet is kept in an enclosed environment, such as a car, the risk is even greater. In most cases outside temperatures won't get out of the low 100s to 110s. However, in a parked car the temperatures can heat up by 40 degrees F within an hour and can get up to 150 degrees; 80% of the increase is in the first half-hour. And cracked windows don't significantly decrease the temperatures or slow the rate of increase.
Heat stroke can be deadly. Whatever the cause (lack of shade, being in a parked, car, etc.) core body temperature can rise quickly, getting into critical ranges within minutes. Very old, young, or debilitated pets are at the greatest risks, as well as those who have dark-colored fur (remember, darker colors absorb more sunlight). When body temperatures get above 105, proteins can begin to break apart and brain cells can die. I've seen pets come in with temperatures that are above the normal range for a thermometer (generally meaning 106 or higher); most of those didn't survive. When body temperature get this high, even if a pet survives there can be permanent brain and organ damage. Besides the immediate danger of brain damage, there can be other serious concerns that may not show up until a day or two later. Simply put, overheating can be deadly.
This is an entirely preventable problem! Don't EVER leave your pet in a car. There have been cases of death when outside temperatures are as low as in the upper 60s (remember...around 40 degree increase means that at 67 outside the inside temperature can get to 107). I don't care if you crack a window, put the sun shade up, or take other measures. DON'T leave your pet outside in a car for even a few minutes. If you come back and your pet is dead or in serious condition, YOU are the one who did that. Also, don't ever leave your pet outside without any way to get in the shade and out of direct sunlight. If you have a shade-free yard, don't leave your pet outside for more than a few minutes, and keep checking on them regularly.
Take care of your pets in hot weather. They may be in situations that they can't control but we can. Be aware of these circumstances and you can prevent serious harm or death.