Since I officially suck at explaining, the pictures may help you more than my description of the step.
Also, since the bottom of the heart opens, you can also use it as a book mark.
Step 1: Step 1: paper
Cut it into two connected squares.
Step 2: Step 2: creases
Step 5: Step 5: fold flaps toward vertex of the triangle
Step 9: Step 9: start the decoration
Step 10: Step 10: almost done
Step 11: Step 11: finishing touches (extra help)
Use it as a Valentine's card or rip it up to show your hatred toward love, or do whatever your heart desires :)
Also, I published a video on how to fold this on Youtube, check it out if you still need some help: