Personally, I would probably slice it into steaks of a sort and pan-fry it in pasture butter with garlic and onions. After frying it, I would add some cream and madeira to the pan and create a sauce for it. No idea how it would turn out, but I imagine it would be passable.
I recently made beef heart bourguignon and it was delicious. There many recipes on internet; just omit the flour and it is still fine. I did something like this.
1) cube and brown meat (I used tallow)
2) cover in dutch oven and braise in wine and stock on very low heat until tender
3) cooked bacon in separate pan, then added that
4) cooked mushrooms and onions in bacon grease, added those
5) thyme, bay, salt
6) some parsley sauce for serving
Beef heart is a little tougher so I like it slow cooked this way or ground up and mixed with regular beef for chilis and other ground meat concoctions. You can marinate and cook it fast, but hearts of smaller animals are more tender and turn out better this way.
From what I understand, it's either fast and hot, or low and slow, though I've heard many people say that it's great marinated and grilled. I've only made it in the crock pot (on low) and it turns out decently well, but I have plans to try it in a stir fry, and possibly in a stew.
I cook mine through (low and slow), and I can't imagine that leaving it pink would make it more tender (having sliced up two hearts so far, it's very tough even raw), but there's no harm in trying it!
I ran it through the food processor. It made excellent patties, in fact anywhere you would use ground beef. It's a fair lump of an organ and you end up with a heap of meat for a few dollars. Excellent value..