My husband has had pain on his left side under his rib cage he is in a lot of pain what could it be ?

Pain is a very difficult ailment to pinpoint... describe the pain: is it stabbing, is it throbbing, does it hurt when he breathes in deeply, or does it hurt near the back/front, does it hurt when he lays down, etc.

In that general area, the heart, spleen, and the pancreas are nicely aligned... which means that it could be any of those. Of course, it could also be his ribcage, his muscles, his back, etc.

Has he been hurt before? Is he on any medication?

It does not hurt worse to lay down he said that it is like pressure not on any meds and he has really bad heart burn so bad he can't even drink water and he said that it hurts somrtimes when he breaths in but not all the time and it is swollen to

What's swollen? His left side is swollen?

Yes right under his rib cage

Swelling usually means an infection or a trauma of some sort. I suggest he gets a doctor to take a look at it.