We have always used both the heart and the liver. Normally the liver is eaten the same night the animal is taken. Flour and fry it up with a lot of onions, take it out of the pan, scrape up the bits of fried flour, stir in a little more flour if needed and then put a little milk in the pan to make some sawmill gravy to top it with. It is a tradition with the crew I hunt with.
For the heart we clean and trim the top of it, slice it about 1/2 and inch thick, roll it in flour seasoned with a little salt and pepper and fry it. I like it with eggs for breakfast. I've also eaten the tongue but really didn't care for it with onc exception: buffalo tongue is superb.