Here is a very brief plan of action for quickly dealing with the escalating effects of environmental heat:  

Heat Cramps: Replenish fluid and sodium balance with foods and drinks that contain electrolytes, such as sports drinks or salted snack foods.

Heat Exhaustion: It's time to take a break. Rest for a while and apply cold packs or wet towels to your skin. Find a seat in the shade or in an air conditioned environment. 

Heat Stroke: This is a medical emergency and needs to be dealt with immediately. Rapidly cool the body through any means available, administer IV fluids and transport the individual to an emergency department.