I've been meaning to do this in ages, but the joys of motherhood were keeping me busy till today. A heart-shaped bokeh attachment (or any other shape, for that matter) is very easy to make:
1. Take a sheet of heavy stock paper.
2. Take the cap off of your 50mm lens (or any other lens with a high f-stop) and put the lens on the paper, glass down.
3. Outline the front of the lens and cut it out.
4. With the help of a paper-punch (if you have one) or a utility knife, cut the desired shape out from the middle of the circle.
5. Place the circle at the front of your lens, as you make sure that no light escapes from the sides.
6. Find a tree and set your subject in front of it - tree crowns make wonderful daytime bokeh. Christmas lights or traffic lights would do for night time shots.
7. Shoot open wide and enjoy!
The photos below are really just test shots; it is too hot today and I didn't feel like going on a long walk so I just stepped out my front door and used what's there. My succulent and my cat provided the rest!