The night before a scorcher, I move the plants that can be moved to areas that will be shady during the day.
I've also begun the routine of watering thoroughly every night. I'm going to continue doing this until the end of Summer. The idea is that this gives plants several hours to soak up moisture without the sun soaking it up instead. Since I've been doing this, I haven't had any plants die due to the heat.
My suggestion to those of you experiencing heat waves is to take up the habit of watering thoroughly between 8 p.m. and midnight.