i put chopped ox heart in my stir frys. my flatmates think it's yum but i haven't told them it's heart. 
lambs hearts are good roasted especially if you pack the aorta and pulmonary artery with garlic and rosemary. 
as for my fish, i chop it up into little pieces, and wrap little chunks in glad wrap and freeze. when comes time to feed, drop the frozen ball into a cup of water, let it defrost, take the glad wrap off and let the fish have it.