Go easy when it comes to exercise, especially if your pet is not used to it. Aim for the morning or evening when it temperatures drop.
Make sure they have enough water, whether it be on a walk or in their water dish at home. Panting is often a sign of thirst, so be sure to keep an eye out for that telltale symptom as well!
If they stay outdoors, make sure they have shade and their water is kept in the shade as well (and is consistently filled).
A few signs of heat stroke
Temperatures of 105-110 degrees, excessive fast panting, loss of strength (staggering, unable to stand etc), dark/bright red tongue/gums, vomiting, and coma are a few warning signs of heatstroke. If you think your pet may be suffering from heat stroke, it is imperative to seek the help of trained veterinary professionals right away.