I think our heart's desire has to do with putting ourselves to God's purpose.  It's like we're this particular kind of tree that God made and our purpose is to bear a certain kind of fruit. 

And if we watch ourselves and the things we do and the things we are interested in and the things we have fun with and the people we like, why then we can ponder all that and see what kind of fruit tree we are.

That is our hearts desire, I think. And God wants to water us, feed us and nurture us so that we bear the fruit we were created to produce.  Then we will be happy.

This is really good, thanks!  I've thought a lot about this in recent years!  ...and I come to agree with @sometimestheycomebackanyway@xanga - that our desires and God's purpose are aligned (although its clear to me that's not a no brainer...and what I've only come to believe in this season of my life).

What if its true that we're each made as a good gift...and the hope of life is to discover who we are.  Perhaps the way we discover who we are IS to pursue the desires of our heart...AND delight in the Lord.  Or as the verse says "Delight yourself in the Lord AND (not if, or on account of, or then...check out original Hebrew, with word definitions in Blueletterbible.com) He will give you the desires of your heart."  And no need for hedging in any way...ie, no reason to pursue desire within reason.

And what if Jeremiah is right...that the heart is a labyrinth and is difficult to 'know' (as in the Genesis interpretation of Hebrew into the English word 'to know'), meaning 'to know intimately' as in intercourse in marriage is a metaphor for deep human intimacy (naked and vulnerable, most fully known of any human relationship, but intimacy growing in a life journey together).

What I've discovered as I've pursued the desires of my heart in recent years is that there is a deeper desire beneath the one I'm pursuing.  One that's more foundational...and yet only discoverable by pursuing the desire that I can feel.  My desire for a '66 corvette is good, and yet I've discovered the desire beneath that desire is to be seen.  That desire is good, and yet the desire beneath that is to be viewed by others as a performer.  And that desire is good, but beneath that desire is to have my gifts be seen....and so on until what I can so far see beneath all my desires...and that is love.  I desire to love and be loved, and I to find it I need to 'hang on tightly and let go lightly' The Croupier (1998 movie with Clive Owen).

In this moment of my own journey I can only intellectualize that thought...and, of course, its 'Biblical'...but I don't think I've yet fully internalized it.  The hope for the spiritual or life journey, I've come to believe, is to become Holy, authentic...to intimately know myself and to know God.  And that journey is NOT made easier by being a good boy, or by doing it 'right' or by walking out the perfect path, but the journey to know the human heart, I believe is necessarily messy with false starts, dead-ends, long boring straightways, twists and turns...if we truly desire to know ourselves and God.  He (and therefore we, if we're made in His image) are a mystery!  Praise the living God!

"The world breaks everyone and afterward many are strong at the broken places.  But those that will not break, it kills.  It kills the very good, and the very gentle and the very brave impartially.  If you are none of these, you can be sure it will kill you too, but there will be no special hurry."  Earnest Hemingway, A Farewell to Arms (1929)

@Doubledb@xanga - rereading your comment...I wonder if you'd agree with my comment.  If you're willing to have a conversation I'd be interested to discover common language (if it exists) to navigate this concept across cultures, ie both Church-going Christian culture and 'meaning-of-life' seeking secular culture.