For the OP, my horse( sunny) Isnt BUILT for Barrels either. But he has the heart. I am STILL in the process of trotting the pattern( loping a bit to) I am going REALLY slow with him now.. because he may have a harder time my vet said. So I say.. If your horse has the heart.. Go for it.. just be cautious. Pay close attention to if he becomes "off" or something seems to start to bother her. Go very slow.. SLOW..
Maybe prove all the above wrong hehe;) and the statistics of course.. .. but yeah.. Im in the process.. You work with what you've got, I can't go out and buy another horse, so Sunny's going to have to work..