The Heart Pillar is most likely on the 3rd floor in Flopside. If you don't know how to get there, use Fleep on the dimensional rift on the 1st floor of Flipside, which is near the Card Shop. Follow the path, and you should be in the Mirror Hall. Solve the puzzle using the clue (not telling where it is :)), and you will be in Flopside. Flip to 3D, follow the path, and use the Up elevator to get to the 2nd floor. Then, go up to the 3rd floor using the Up elevator. You should see the Heart Pillar up ahead.