1 - drip irrigation and heavy mulch for uniform moisture

2 - afternoon shade

3 - royal chico reportedly takes heat and matt's wild cherry is taking over my yard. Matt's is a tiny cherry tomato, grows in small clusters, sets fruit and ripens almost all year.

Most "heirlooms" are from moister, cooler climates and probably can't tolerate the heat.

If you want to experiment, find some roma tomatoes from mexico this summer and save the seeds. They aren't the true roma variety, they are a paste tomato developed to tolerate the heat of the sonoran coast.

Your other alternative is to grow the extreme short-season tomatoes developed for canada so you can get a crop in spring and fall, skipping the summer heat.

Thanks. I have them on drip irrigation, on the east side of the house (afternoon shade). I'll try mulching some more.
I did a little research, I think I'm going to try Sioux tomatoes.
I might try a cherry tomato (I'll look for Matt's wild cherry), but I use mine mostly for cooking.

I am growing heirloom tomatoes for the first time in the desert this year (moved from Philly to Albuquerque). My soil is not where it needs to be yet and I have had a lot of problems with several of my plants. Oddly I've had some foliage disease despite the single digit humidity. Some heirlooms are more susceptible than others. I have also experienced terrible blossom end rot, something that has started to correct itself, but most of my first flush of fruit was marred by this problem. I have even moisture and mulch, so I am not sure what the problem is. Another big problem was blossom drop, which occurs in high heat. I've probably lost 50% or more of my blossoms on most of the plants. I am also losing blossoms on my cucumber, bean, melon and squash plants. One of my tomato plant's leaves appear to be just burning up in the sun - the edges of the leaves are turning brown and crisp and they are rolling up as it to protect themselves. I think shade is really critical, especially for healthy growth and good pollination. I have one plant receiving half a day shade under a fruit tree and it is by far my healthiest plant, with the most fruit. I will save seed from this plant. The variety is Druzba - from Eastern Europe and it's easy to find as seed, possibly as plant starts. The other variety that is doing relatively well in full sun is Cherokee Purple, which is a U.S. heirloom from the hot plains region. I find it to be one of the finest tasting tomatoes I've ever grown. For past tomatoes, I grow San Marzano, from Italy. They are also doing well in my dry climate. Their flavor is bland until you cook them, transforming them into a luscious, complex sauce. Next year my soil will be better and I will have shade structures in place. Good luck.

One of the best I've found for desert growing is Punta Banda, originally from Baja California. Medium size fruit, great taste. As far as I know, not commercially available as plants, but J.L. Hudson sells seed. I save my own seed and have noticed that over the years the tomatoes are getting larger and larger even though they're grown in an isolated area where hybridizing shouldn't be a problem.