The first heart can be found by following the path from the Hall of Heroes.  Follow the path all of the way to the giant tree.  Start following the ledge and steps around the tree to the left as it climbs in a counterclockwise direction.  You will quickly come to a climbable wall on your left (if you reach the two elevator platforms then you've gone too far).  Climb the wall all the way to the top of the tree and you'll see the heart in the middle of a ring.  This is the ring of the giant sumo wrestler and you'll need to defeat him to get the heart - luckily it is not too hard to do so.

Run in a circle around the outer edge of the ring so that you don't get close to the sumo.  When he leans over, stop.  He'll then pound his fist into the ground - when you see this move or jump quickly to the side.  The sumo will charge but he can't change direction so he'll move to where you were instead of where you are.  When he reaches the edge of the ring he will teeter on it for a few seconds.  Attacking him from behind while he is trying to catch his balance and you will knock him out of the ring.  Do this three times and you will be able to collect the heart at the center of the ring.