Dover Saddlery has a great post about summer riding tips. You and the horses in the heat sounds great to me, but there are ways to make it easier on you and the horse.
Summer Riding Tips
The sunny days of summer bring extended daylight hours and the clear weather that means more opportunities to ride outdoors. But some summer days are so hot and humid that they rightly cause us concern over the potential for heat-related health consequences— in our horses and in ourselves.
How much heat is too much to ride your horse? What can you do to keep your temperature regulated while working in the barn or riding? Here are some suggestions for preparing you and your horse to deal with high summer temperatures.