Heres the solution to your problem. Frost damage will drop the blossoms. I doubt that is the case. Heat won't do it, really. It's calcium deficiency.
Here is your solution:
1.
Mix 2 Tablespoons of EPSOM SALT with 1 GALLON OF WATER.
Shake it up very well, and water your plants being affected. Not too much. Water with plain water afterward to get it mixed well into the soil. Do this once every month.
2.
Add crushed egg shell. Everytime I plant my tomatoes I put a handful of crushed eggshell under the root system.
3. Add oyster shells.
3. Make sure they aren't too watered. Water them once every 3 - 5 days (depending on the heat) extremely thorough. I do this every year and end up with a surplus of tomatoes, plants, and peppers! People generally come to me with simple help and solutions like this.