Make a pattern by cutting out a heart shape from wrapping or tissue paper. Make the paper pattern just slightly larger than the size you want your finished chalkboard to be. (If you want to be able to fold the chalkboard over some chalk to hold it inside, practice with the chalk you plan on using. Adjust the size of the heart as needed.)
Cut two fabric hearts using the paper pattern as a guide. One should be cut from a chalkboard fabric. Cut the other from a fabric that you want to use on the other side/outside of the chalkboard.
Using a serger
Place the fabric hearts together with the right sides facing out (wrong sides together). Using an overlock machine (serger), sew around the edges all the way around the heart.
Using a regular sewing machine
Place the fabric hearts together right sides together (wrong sides facing out). Sew around the edges of the hearts, leaving an open area around 3 inches long on one of the straight edges of the hearts.
Reach in through the open space and pull the hearts right side out.
Fold down the edges of the open space, and sew across them to close up the gap. To finish the edges of the chalkboard, sew all the way around the heart a few millimeters from the edges.
Folding the chalkboard
To fold the chalkboard into an envelope shape, fold it in thirds, folding in either side over the center. (You can place chalk pieces in the center to hold them in place.)
Fold the top of the heart down over the center.
Fold up the bottom v over the rest of the folded heart.
Adding a closure
With the heart-shaped chalkboard folded into an envelope, plan where you want your closure to be. You can use plastic snaps on both the bottom point and the center top. If you prefer to close it with an elastic band, sew a loop of elastic to the bottom point of the heart. The loop should be just large enough to fit over the folded chalkboard to keep it shut.
Notes
You can make a cute heart-shaped eraser by cutting out a small heart from felt. Cut a slightly larger heart from craft foam and glue the hearts together. If you'd like the connect the eraser to the chalkboard, glue one end of a piece of cording between the felt and craft foam. Sew the other end of the cording into one of the seams of the chalkboard heart.