Use the Mover tool or Pick tool to move the copy of heart to the right and down a little from the first heart. See example above.
Make the heart on the right the active layer (Copy of Merged). Use the Magic Wand to create a selection (tolerance 20, anti-alias checked, but no feather). Click the background space around the heart, hold the Shift key down and click the interior of the shape. Invert selection ( Selections > Invert ). Let's also tighten up this selection a bit. Selections > Modify > Contract. Enter 1, and click OK.
Make the heart on left the active layer (Merged). The selection marquee should still be around the heart on the right. Select the Eraser tool and set the options for:
Size: 5-10
Hardness: 100
Step:10
Density: 100
Thickness: 100
Rotation: 0
Opacity: 100
Erase the part of heart on that we want to cross under the other heart. The area you need to erase is shown in the image above. When you're done, go to Selections > Select None.
