So this is very easy but still it looks great :)
Cut the strips of paper..
Take one and fold it in triangle as in picture 1, then fold it again and again and again..
..until you get this:
Make sure that you remain section that you didn't fold and cut his corners as shown, then push it into a part which is raised in the third picture. At the end you should have a triangle as shown in the fourth picture.Take a triangle and press it with all three sides to be 'bloated' and you get the 3D effect.
Still does not look like a heart, right? Well, take scissors and cut out the sharp corners in a semicircle..and that's it :D
It's fun and cute, try it :)