You'll need some wood hearts (I found mine at JoAnns), a ring shank, some wood glue, gloss sealer and a woodburner.
Simply trace initials or a word on the heart then burn it using a fine tip on your wood burner. I also burned the edges of the heart with a flat tip. Spray it with gloss and let it dry. Use wood glue to attach it to the ring shank and yer done!