Phoenix's recipe looks great, but if you want something simpler but still delicious, try this:
I just remove any excess fat (snip off with kitchen scissors) and cut out any remains of vessels (which will be too tough to eat). Then enlarge the cavity by cutting through the central division, and stuff with sage and onion stuffing, forcing in as much as you can. (Home made stuffing is best , but Paxo also works well and Tesco's own brand is cheap as chips). Put 2 heaped tablespoons of Bisto Best Beef gravy mix into three quarters of a pint of hot water, and stir to make a gravy. Put in a casserole with the stuffed hearts and cook in a pre-heated oven for an hour at about 170 degrees.
The stuffing will spill out into the gravy and make a lovely thick herby sauce. Serve with vegetables of your choice. Scrummy!