Our experiences in this life (and in past lives) shape how we view our heart and how we relate it. We can become kind of tough, kind of cynical and we loose a sense of our "Buddha nature". But no matter how disconnected we become, our essential goodness never really leaves us.
If you put a $100 bill in the pocket of a winter coat and forget about it, but then, a year later when the snow comes, you rediscover that hidden treasure. You think "wow, I'm so rich , wow, what a great day !' Well, your Buddha nature, the essence of your heart, is just like that, always there to be discovered. It's far more valuable than a $100 bill, in fact it's more valuable than all the wealth of the earth.
Coincidentally, I wrote a poem about this back in 1997 and only today , re-discovered it. I call this poem "unearthed".
from a fathom of black solemn soil
soaked in frail mis-understanding.
Ragged and cracked
it is really a hollow bone
to it's terrain
which is sweet