Here is another worthwhile article that Rodney found in the GWRRA newsletter:
Heat related illnesses are extremely dangerous. The symptoms and causes are gradual and can accelerate to the point that can cause your body organs to function improperly. The biggest cause of heat related illness is dehydration. Without the proper amount of fluids and salt, vital organs like the kidneys, brain, and heart cannot function. Your blood thickens and your heart pumps much harder to circulate blood throughout the body.