My Father Has Serious Heart Damage. When He Eats, It

My father has serious heart damage. When he eats, it causes him so much chest pain, is it because
the stomach swells when full and presses on the heart that is struggling to pump? It doesn't seem to bother him as much during the day, but when he lays down to sleep, he has to take alot of nitro. He is 83 and is told he has two arteries 100% blocked and two 80% blocked. The viability study shows he can not have bypass surgery. Does he need to go to a gastroenterologist for the pain, or is it heart related, and there is nothing to be done? I just want him to be comfortable.