Chickens are quite vulnerable to heat; it's actually harder on them than freezing winter temperatures. If you notice yours are panting and have become lethargic, try to provide them with a shady area away from the direct sunlight, replace their water often, and feed them (just layer feed-scratch will raise their body temperature) in the early morning and evening after it cools down. Metabolizing their food makes them hotter. Plus, like us, they just aren't as hungry while it's hot.
In some instances, it's good to put a fan inside the chicken coop to keep the air circulating. Some people like to use a chicken tractor so that they can move their flock to cooler areas as the day progresses. It's likely that egg production will go down some during the hottest summer days.
It's best to refrain from petting or handling your birds during a heat wave. They'll be better off if they're free to go where they're most comfortable and 'chill '. Calm birds stay cooler.
Where I live temperatures are lower than many areas (especially this year), so if you have any tips or secrets for hot weather flock management, do please share for the benefit of others.