Like I said, environment is everything. All the meds help with an acute crisis.
My first heaves horse was symptom free until the day he died, age 26, of heart failure. My second, due to bad circumstances( no possibility to keep her outside, ignorant people who thought moldy hay and straw were no big deal), died of heart failure age 15, a day before the vet appointment to have her pts.
I didn't mean to sound harsh, but what happened to my little mare I don't wish for any horse.
This is why I see it the way I see it.
If you don't have an alternative to the current barn, see if you can convince them to use slowfeeder nets for the hay ( you said there were other horses sharing her pasture). It would save hay, too, btw.