Welcome to the forum! I know you'll get lots of advice on your tomatoes from the friendly folks here!

Now let's see...
First of all, don't give up yet! Tomatoes can be a little strange - they often exhibit signs of thirst when they're actually getting TOO much water.
Tomatoes need 1 to 1 and a 1/2 in of water a week, the best way to accomplish this is one deep watering, rather than several shallow ones. If possible, it's best to use a soaker hose or drip irrigation, as this lessens the chance of fungal diseases caused by damp foliage.

You say you're having a heat wave, tomatoes will sometimes react to the heat of the day by curling and wilting. If this is the case, they will wilt and curl their leaves during the hottest part of the day, but will bounce back at dusk, during the night, and in the early morning. The curling of the leaves is a defense against excess transpiration (loss of moisture). You can check yours at those times to see if this is the case.

Well, there's a couple of ideas to get you started, let us know what happens, okay?

Nikkal