I haven't posted in a long time, because many of the attitudes here are very strange.
First , beef heart is affected as much by quality of handling as anything. If it is not shown the proper respect by the butcher, you can get a pretty off tasting product. However if you get a good one and freezing does not harm it, it will be quite good.
One quy posted that it is tough and needs slow cooking. My answer to that is buy new teeth
Since, it is one of the organ meats, be aware it is very nutritious.
My daughters love it. There are many ways to prepare it. I sometimes put it in a frying pan with a little butter and sliced onion and when it is still a little pink in the middle serve. Oh by the way I did cut them in strips and wherever they curled I would slice across the muscle.
or.... I would place it in a pan with water and seasonings and boil for a while, but not too long, then rub with olive or coconut oil and throw it on the grill.
The possibilities are quit varied.