I saw some hearts similar to these at a local home decor store. I wanted to buy some, but I knew I had all the supplies and that I could probably make my own! The ones at the store were Red, which were really, really cute, but I didn't have Red yarn so I used what I had.
First of all, trace or draw a heart shape on some styro foam. I used some styro foam that had come in a box with dishes in it... good way to recycle, right?
Next cut out the heart. I used my super nifty heat styro foam cutter, but you could use a knife.
Now use hot glue and begin wrapping your styro foam heart with yarn.
There you have it... some really easy, inexpensive, light-weight Valentine hearts to help add a little bit of fun to your holiday!
Enjoy. (Sorry these pictures aren't the best. The lighting wasn't very good.)