The summer is just around the corner. Rabbits in the wild live underground and are not out in the heat of the day.
Protection is vital against the heat of the sun, many rabbits every year are dying from heat stroke. Hear are a few helpfull hints on
protecting your rabbits.
Heatstroke most commonly occurs when temperatures are 82° or above. High humidity (over 70%) can also increase the likelihood of heatstroke. Other risk factors include inadequate shade and ventilation, overcrowding, and other forms of stress.The signs of heat stroke are as follows.
Panting
Bright red tongue
Slobbering, or thick, sticky saliva
Depression
Weakness
Reluctance to move
Convulsions
Fast, shallow breathing
Hot ears
Listlessness
Wetness around the nose area
Tossing back of head while breathing rapidly from open mouth. 
Ultimately, death
What to do, remove your rabbit from the hot area and contact your vet
wet ears feet and fur with cool water. Do not put the rabbit in water as cooling them down to quickly can cause life threating problems.
Your vet will lower your pet's body temperature to a safe range (if you have not already) and continually monitor his temperature. Your pet will be given fluids, and possibly oxygen. He will be monitored for shock, respiratory distress, kidney failure, heart abnormalities, and other complications, and treated accordingly. Blood samples may be taken before and during the treatment. The clotting time of the blood may be monitored, since clotting problems are a common complication.
things to keep your rabbit cool are, tiles layed in their cage to lay on , ice cubes in their water bottles, misting of their ears.fans , air conditioners, umbrellas over the cage.
Place the cage in as much shade as possable, if the cage is in a shed then ventilation is vital.
I am testing out a sun screen to keep my rabbits cool. Its a aliuminum grrenhouse shading that sould reflect up to half the heat away from my cages. Will let you know later how good it is.