My horse suffers from pasture related heaves so turning her out is a big NO. She breathes better in the barn in the summer months.
I am trying a product this year called Clarity (smartpak.com) It has gotten a lot of good reviews. It's supposed to taste pretty bad, but SmartPax is sending me a 3 day supply to try on my mare first to see if she'll eat it.
I also use Dex. She did pretty well last summer on 5cc orally daily.
I hate heaves. But at least there are some things I can do to help my horse breath better.