Not sure what you mean, sometimes tomatoes get sunburnt on the top, one side etc when it is really quite hot if there isn't enough leaf protection. I have been having that problem a lot the last week or so. Just cut the hard sunburnt part out and enjoy. Note, many heirlooms ripen a bit irratically compared to tomatos you see in the store.
I'm not sure exactly what causes that, perhaps a little sunburn or irregular watering or whatever, tomatoes are sensitive to a lot of different conditions. But I've seen it frequently, it is quite natural, not a sign of bugs or disease, and your tomatoes are perfectly safe.