I would cut it into strips and try to keep the grain a short as possible, then cook it very very quickly on a grill. Or, I would cube it and cook in something like a stew which cooks much longer and will soften it. You just want to keep it from turning into shoe leather. Something that works as hard as a heart is going to be tough.
The woods are lovely, dark, and deep, but I have promises to keep, and miles to go before I sleep, and miles to go before I sleep.