Why do they say you have a "broken heart"

I was thinking about this one today and wondering - why do they say you have a "broken heart?" I feel like it should be a "broken head." Maybe that sounds kind of gross, but it's true. Because it's your head that feels broken when you hear a song that reminds you of the person you loved that didn't love you. It's your head that feels broken when you see a picture of a time when you were happy and realize life will never be like that again. It's your head that generates the tears that stream down your face as memories of all the things you shared come to mind - the smiles, the hugs, the kisses, the laughs - things that will never happen again. So I guess now when people ask how I'm doing, I'll them my head and my heart are broken. And only time can heal both.