HillaryRose,
You will always get lots of friendly and supportive advise, here.
I cycle in the heat regularly. But the potential for a) heat exhaustion, and b) heat stroke, is always there.
Heat exhaustion is related more to depletion of electrolytes (sodium, potassium). It is uncomfortable, but not deadly. Restoring electrolytes will bring about recovery.
Heat stroke is another matter. Temperature regulation becomes ineffective. The body temperature rises so high that brain tissue begins to die. It is life threatening. To prevent heat stroke, keep body temperature down. Ways to do this include cycling at an easy pace, drinking (I use very cold water, but cold water can pose a health threat of its own for asthmatics and those with atrial fibrillation, a heart rate irregularity, usually diagnosed by a doctor), taking breaks (in the shade), and knowing when to quit.
Check reference resources for all the potential symptoms of heat stroke to be well-informed beforehand.
All in all, while it's good to be prepared, cycling in the heat can be enjoyable and quite safe. I believe it's easier to stay cool on a bike than it is while walking or standing in the heat.
