First, cut out two identical heart shapes in your choice of fabric. I recommend folding your fabric in half and then cutting a half-heart (a la elementary school paper valentines!) for symmetry, then tracing the second from the first.
Clip your curves and corners and trim the edge to 1/8", or use pinking shears. Do not trim where your seam is open, and make sure you do not cut into your seam.
awl to get your corner crisp. Make sure your unsewn edge is folded in evenly. Press.
Topstitch all the way around the heart, closing up the hole as you go. If you want this to be a patch instead of a pocket, you can skip this step.
Pin the heart where you want it go.
Stitch along the bottom half of the heart directly over the topstitching, backstitching both ends. All done!