I bought a beef heart and there was hardly any fat on it at all. Instructions I read online said to cut it off along with the connective tissue that it's attached to all around the heart. I spent the whole week eating my beef heart last week. I don't have any answers for you about what qualities the fat will have. But I have read the heart itself has a lot of CoQ10 so maybe the fat has some, too.
Female, 5'3", 49, Starting weight: 163lbs. Current weight: 135 (more or less).
I can squat 180lbs, press 72.5lbs and deadlift 185lbs