Here's how to sew a heart, using template #3 (at the end of this tutorial).
1. Using a pencil, trace around the template on the WRONG side of a piece of fabric. This pencil line will be your sewing line, so you need to leave about 1/4" of fabric all around the heart when you cut it out.
2. Add some decorations to the front of the heart before sewing it to the back.
3. Place the heart FACE DOWN onto the backing fabric, so the RIGHT SIDES of the fabric are facing each other. If you want to add a ribbon or baker's twine to the top of the heart, insert it into the seam now, before sewing. Here I have cut two 12" pieces of baker's twine, folded them in half, and taped them at the fold. The taped part will extend outside the sewing area, and the untaped part is curled up inside the heart halves. Note the two pins in the picture; the area between the pins will be left unsewn for turning the heart right-side out.
4. Sew all around the heart on the pencil line, leaving an opening for turning. When you have finished sewing, clip the fabric at the top of the heart, right here in this spot where it dips down and forms a "v". Clip almost to the sewn stitches, but don't cut through them!
Here's my heart, ready for turning. The hemostats and chopstick are handy for turning it right-side out.
5. Turn the heart right-side out, with hemostats (pictured) or your fingers.
6. Shape the top curves and the bottom point with the chopstick.
7. Iron the heart, paying attention to the unsewn opening; you want to make sure the fabric there is a smooth curve.
8. Stuff the heart with polyester fiberfil, and sew the opening closed by hand.
I tied the baker's twine into a bow. Looks nice!