The 2013-2014 winter went down as one of the worst in history for most of the United States. It seemed that the stormy cold weather might never end. Meanwhile, here in California, most of the winter consisted of blue-skied, 70-degree days.

The irony is that each part of the country would have preferred to have the other’s weather. Folks in the Midwest spent the winter digging themselves out from snow that we here in California would have been happy to have, since we’re in the midst of an historic drought.

This brings me to two points. First, the grass is always greener on the other side of the fence. And second, no matter where in the U.S. you live, winter is now over.

The end of winter, however welcome, also brings with it certain threats. And for dogs one of the greatest threats of summer — especially the early summer — is heat stroke.

Heat stroke is a condition, as the name would imply, in which the body becomes overheated. Even with aggressive treatment it is often deadly.

There are several risk factors for heat stroke. For instance, heat stroke is more common on the first truly hot day of the year. The reason for this is acclimatization. Over the course of the summer, dogs acclimatize to the heat. This is a fancy way of saying that they become better at maintaining their body temperature through panting (which is their equivalent to sweating).

In the early summer, there has been no acclimatization. There has, however, been no shortage of cabin fever. On the first really toasty day of the year, many people feel a nearly irresistible urge to take Fido out for a run. Resist that urge.

Other dogs suffer heat stroke after being let into a yard with insufficient shade early in the morning, when it is deceptively cool. By the time the owners come home from work, the dog has been overheating for hours.

And of course, dogs left in cars are famously likely to develop heat stroke. On even a warm day, let alone a hot one, it is not safe to leave a dog in the car even briefly. I have treated dogs whose owners left them unattended for just a few minutes while they ran into a shop. By the time they returned the dogs were in severe distress.

Not all dogs are equally susceptible to heat stroke. I already mentioned that acclimatization plays a role. Where I live with my pal Buster the mercury rarely tops 75 degrees. If in August I took him 50 miles east, where it’s 20 degrees warmer, to play fetch he’d likely collapse while local dogs in the field cavorted without issue.

Age, breed, body weight, coat color, and physical condition also affect heat stroke susceptibility. Young dogs are less likely to suffer from heat stroke than their older counterparts. Brachycephalic (short snouted) breeds such as Bulldogs and Pugs are at greater risk than those with longer snouts. Overweight dogs are markedly more likely to develop the condition. Dogs like my pal Buster with black coats are less heat tolerant than those with lighter coats. And physically fit dogs are less prone to heat stroke than their sedentary counterparts.

Heat stroke is a condition that affects the entire body. As the dog starts to warm up, he pants desperately to try to bring his temperature down. Panting, as I already mentioned, is the canine equivalent to sweating, and dogs lose a great deal of water as they pant. Dehydration therefore starts to set in, compounding the physiological stress of being overheated.

The physiological stress caused by overheating is severe. Organ damage and neurological compromise can occur. The heart, kidneys, and brain are especially susceptible to the ravages of heat stroke. Respiratory distress can progress to lung damage. Blood cells may start to burst, blood vessels may start to leak, and the hematological issues can progress to a condition called disseminated intravascular coagulation, or DIC. Multiple organ dysfunction syndrome, or MODS, is also common. DIC and MODS are every bit as bad they sound.

Treatment for heatstroke involves cooled intravenous fluids, exterior cooling of the body, and supportive care. Blood transfusions or other significant interventions may be necessary. The prognosis is guarded, even with aggressive treatment. Many dogs require several days of intensive care in order to recover. Others don’t recover even after days of intensive care.

Heatstroke falls heavily into the category of conditions that are better prevented than treated. The key to prevention is awareness. Be familiar with the weather forecast, and plan your dog’s outdoor time accordingly. Make sure that plenty of fresh water is always available. Avoid the sun and activity in the heat of the day. Don’t leave your dog unattended in the yard or especially in the car.

And finally, remember that heatstroke can affect any dog. It may be most common in overweight elderly Bulldogs on the first hot day of the year, but it also can strike fit young Labs late in summer.

Have fun with your dog this summer, but be safe, and be aware of the heat.

Learn more about dogs with Dogster:

• 6 Ways to Thwart an Off-Leash Dog Rushing You and Your Dog
• On Dogs and Body Language: How I Learned to “Speak” Dog
• Aspirin and Ibuprofen: Are Human Pain Meds Safe for Dogs?

Got a question for Dr. Barchas? Ask our vet in the comments below and you might be featured in an upcoming column. (Note that if you have an emergency situation, please see your own vet immediately!)