I cooked up two deer hearts this year and for both I just cleaned them up, trimmed the fat and connective tissue, then cut them into roughly 1-2" squares. Then I tossed them in olive oil along with salt and pepper, and proceeded to pan sear them in a smoking hot skillet to put a nice sear on the outside and leave them medium/medium-rare on the inside. Ate them along with the tenderloins and the flavor was the same, but if you overcook the heart it will get chewy in a hurry.
I'd never cooked deer hearts before and no one I was cooking them for had eaten one, but everyone said they liked it and would eat it again with the exception of the squeamish 14 year-old who saw me preparing them. The 4 year-old (whose mother is a vegan) thought it was great and kept asking for more.
I had mine Sunday night for din-din and it was absolutely delish. At the last minute of cooking I like to drizzle a little balsamic vinegar over it to finish it off. It browns it up nice and gives it a nice little tang. Definitely, if you're willing to try it, treat the outer skin as silver skin and remove it as Mickey the Dragon did.