Ice Cream & Mashed Potatoes

We have all experienced unfulfilled desires. Yet, God promises in Psalm 37:4 to give you the desires of your heart. Does this mean that, if you desire a billion dollars, a super-model spouse, and death to your enemies God will give you those things? Of course God's word doesn't teach that! So what does the bible really mean when it says that God promises to give you the desires of your heart?