This section is from the book "Economical Cookery", by Marion Harris Neil. Also available from Amazon: Economical Cookery (1918).
1 beef heart
2 tablespoons (1 oz.) butter substitute
1 tablespoon chopped onion
3 tomatoes, skinned and chopped 1 cup (1/4 lb.) bread crumbs
1 egg, beaten
2 tablespoons milk 1/2 teaspoon salt
1/4 teaspoon pepper 1/2 teaspoon celery salt 1/2 cup (4 ozs.) drippings
1 cup (1/2 pt.) stock or water
Beef heart is considered coarse and indigestible, but it can be made palatable by being stuffed and carefully roasted or braised. Remove lobes and all pieces of gristle. Wash heart in several waters, allow it to lie in cold salted water thirty minutes, and then wash again. Cut away membrane which divides the two cavities, and be careful that inside is quite free from blood. Melt butter substitute, add onion, cook three minutes, add tomatoes, and cook ten minutes. Cool, and add bread crumbs, egg, milk, and seasonings; place this stuffing in heart, tying piece of greased paper over to keep forcemeat in. Melt drippings in roasting tin, place in heart, and roast in hot oven two hours, basting frequently. Remove paper, place heart on hot platter, and make a gravy in pan with stock or water. Serve with red currant jelly.
Prepare sheep's hearts in same way as above, cook eighty minutes and serve like beef heart.