Since there are many ways to fold a heart (thanks to all their designers), I can afford to pick one that rewards details that serve my purpose. I chose the following heart because of the back flap which in a way makes it easier to hang/slip into something else, and in my case to hang onto a boat (see more).
1. Divide a square into 3 equal parts.
2. Bring A to align with the nearest 1/3 crease.
3. Bring B and C to align with A.
4. Turn the paper as shown. Fold down the flap behind.
5-6. Curl the sides and tips to shape.