The heart is a muscle that never ceases working, therefore it is fairly firm and free of fat, which is significant on the dietary level. Heart differs according to the animal. Beef heart is large, firm and fairly strongly-flavored. It can be tasty when prepared correctly. Heifer heart, lighter and more tender, is more desirable. Veal heart is very light and tender, while lamb and sheep heart is less refined. 

A little history: North American Indians once reserved the heart of the bison they had just hunted for their chief.