Sweltering summer heat is more than just very uncomfortable for your horse. It's as much a health hazard for your horse as it is for you. Young, old or ill horses are least equipped to deal with extreme heat.
If you've got an aging horse, he may be at risk for heaves, a respiratory disease that makes it hard for him to breathe. Make note of the signs and symptoms of heaves so that you can contact your vet for diagnosis and treatment.
Arthritis in your horse is not a death sentence. Don't despair because you can do a lot to manage arthritis in your horse, giving arthritic horses many more years of comfortable, active and rideable life.