Veronica handles the heat by alternating between sun bathing on the porch and coming inside to lay in front of the air conditioner.
If it's very hot out, she ain't doing nothing. She has quit on walks and we have had to get the car to pick her up. When we did agility before she blew out her knee if it was hot she would either run into the tunnel and not come out or park it in the shade of the A-frame and refuse to move.
She just had her 8 year old annual vet visit with senior bloodwork and was proclaimed healthy as a horse.