Cats can suffer from a variety of heat-related illnesses...heat stroke, dehydration and heat exhaustion.  Of course we are going to advocate the best possible environment for your cat in the summer....air conditioning...but we are realistic to understand that not everyone has or runs them 24/7.  We want to briefly acknowledge (although we don't advocate) the outdoor cat...a cool, shaded area, and plenty of water, freshly filled each day...leave a little water dribble under a faucet if you can. And on really hot days, ice cubes are appreciated!  For the indoor cat, some tips:

In the evening, open windows and use fans to create a cross-breeze, circulating cooler evening/night air through the rooms. As soon as the sun hits the building the next morning, close all windows, blinds, and curtains, and keep doors and windows closed throughout the day until it is cooler outside than it is inside. Then you can open everything up again and cool off to be prepared for the next day. Leaving kitchen cabinets open all night helps too; if you leave them closed, they store the heat and your house won't cool off as much.

Get a 1 or more 3 liter bottles, fill them full of water, FREEZE them but in a manner to not damage them (H2O expands on freezing), then place them in a LARGE bowl(To catch condensate water). Position a fan to blow on these blow upon them. As the ice in the bottles melt, the air cools around them. The fan will blow that air at you. The bowl full of condensate water can be used, if clean, for non consumption use. The water in the bottles can be frozen overnight and used again, repeatedly.

Remember... a cool cat is a happy cat!

If you are unable to take care your cats due to illness or death, do you have a plan?  Do you know who will care for them?  There are many questions that need to be

and conveyed to those who will take over your estate.  Every week the clinic receives calls from next-of-kin wondering what they should do with Aunt Mary's three cats now that she is in a nursing home, or Uncle Joe's 15 year old companion cat, now that he has passed.  All too often, because your wishes were not conveyed, the cat ends up at a shelter, euthanized, or worse yet, out on the street. Something for you to start thinking about now.  Here is an excellent webpage on things you need to consider and get in order now, while you are able:

How Can I Prepare for My Cat's Well Being After I Die?