Heat Stress / Stroke
Ferrets become lethargic in temperatures over 80 degrees. If the temperature does exceed this they are prone to heat exhaustion which can be fatal. High humidity will increase the incident of heat stroke.
To prevent this problem avoid trips in cars in hot weather that do not have air conditioning, never leave a ferret alone in the car even on a relatively cool day as the car will heat up quickly. You must provide a constant source of fresh drinking water and keep cages in a shaded area that is well ventilated.
If your ferret shows signs of heat stress, panting, bright red gums, toungue hanging from the mouth, weakness, muscle tremors, lying perfectly flat or unconcious, take immediate steps, put the ferret in a shaded ventilated area, immerse in cold water and contact the veterinarian immediately.