Asking the Wizard For a Heart

A friend of mine once refered to the heart as "that little muscle that could". Brilliant, I say. What is it that makes it so resilient, and yet so fragile?
From a pragmatic point of view, it's not even useful - aside, of course, from pumping blood. But that's not the heart I'm talking about.

Wizard of Oz (to the Tin Woodman): As for you, my galvanized friend, you want a heart. You don't know how lucky you are not to have one. Hearts will never be practical until they can be made unbreakable.
Tin Woodsman: But I still want one. 

The heart announces itself most poignantly only when it's about to break. And being the generous little thing it is, it takes no one down with it: it falls in utter loneliness. And all of those other parts of your body just sit back and watch while the most breakable part of you... breaks away.

Dorothy: Goodbye, Tinman. Oh, don't cry! You'll rust so dreadfully. Here's your oil can.

Tin Woodsman: Now I know I've got a heart, 'cause it's breaking... 

But also, nothing else in your body is capable of bouncing back like the heart does. Indeed the muscle that could. It hardens with time, and before you even notice it, it's back right into shape. You realize then that the muscle you so wished away is your only foul-weather companion, that no one will ever push you forward like the heart does, even though it's just as down on the floor as you are.

I've always loved The Wonderful Wizard of Oz; and though Dorothy is somewhat annoying, the other main characters are simply adorable. My favorite's always been the Scarecrow, and I've always pitied the Lion. But the one I admire the most is by far the Tin Woodman (or simply Tinman, in the 1939 movie). The guy just wanted a simple flimsy heart. 

"All the same," said the Scarecrow, "I shall ask for brains instead of a heart; for a fool would not know what to do with a heart if he had one."
"I shall take the heart," returned the Tin Woodman; "for brains do not make one happy, and happiness is the best thing in the world."

I pity and admire the Tin Woodman - and I pity and admire the heart. Such a heartbreaking little thing.