The best cooking method for it is perhaps braising. The exception is veal and lamb heart: these can be thinly sliced and fried for a short period of time.
Stuffing heart and cooking it in a pressure cooker is popular.
Demand for heart has plummeted. It is one of the least popular pieces of offal now.
Literature & Lore
“False friends! O, I could eat their hearts with garlic.” — Queen Prezmyra in Eric Rücker Eddison ‘s The Worm Ourobouros. 1922.