You need:
-Dress (preferably not jersey knit, stiffer fabrics work best)
-some sort of ribbon, lace, something to pin around the edges of the cutout heart.
-sewing machine
-pins
-tape
-marker

First, I taped off the dress so that I could draw a proper heart to the right size. I cut out the heart and pinned the lace around the edges (with the tape still on). Then I sewed around the edges, took off the tape, and ironed down the lace and heart. Easy!

Sorry I don't have more pictures-- I get so excited working on a project sometimes that I forget to take photos!