You may use any kind of paper to fold this origami heart. I am using a paper with the same red color on both sides. Make sure the paper that you use is a square (all sides are equal and all the angles equal 90 degrees). The paper I am using here is 20cm x 20cm square one. It is a good size for those who are not experienced in paper folding. If you are become familiar with this model. Then you can try smaller size paper.
Step 1: Square base
01.Let's start with "square base" . Prepare to apply two vertical valley-folds.
02.Apply two vertical valley-folds of the step #1.Prepare to unfold two valley-folds.
Step 2: Inside reverse-folds
03.Unfold previous two valley-folds.Prepare to apply two "inside reverse-folds" .
04.Apply two valley-fold of the step #3.Prepare to open the front-most layer following the arrow
Step 3: Inside reverse-fold
05.Open the front-most layer.Prepare to apply an "inside reverse-fold"
06. Apply the "inside reverse-fold" of the step #5.Prepare to close it.
Step 4: Front-most layer
07.Close the front-most layer.Prepare to open the front-most layer following the arrow.
08.Open the front-most layer.Prepare to apply an "inside reverse-fold" .
Step 5: Start for 5 step
09.Apply the "inside reverse-fold" of the step #8.Prepare to close it.
10.Close the flap.Prepare to turn the model over.
Step 6: Start for 6 step
11.Turn the model over.Prepare to repeat the steps #1-10.
12.Repeat the steps #1-10.Prepare to apply a horizontal valley-fold.
Step 7: 7
13.Apply the horizontal valley-fold of the step #12.Prepare to apply a vertical valley-fold.
14.Apply the vertical valley-fold of the step #13.Prepare to turn the model over.
Step 8: 8
15.Turn the model over.Prepare to apply a horizontal valley-fold.
16.Apply the horizontal valley-fold of the step #15.Prepare to apply a vertical valley-fold.
Step 9: 9
17.Apply the vertical valley-fold of the step #16.Prepare to apply two valley-folds.These valley-folds are 45 degree angle folds and these foldings should be done just below the front-most layer.
18.Apply two valley-folds of the step #17.Prepare to apply a valley-fold and then unfold
Step 10: 10
19.Apply the valley-fold of the step #18 and then unfold.Prepare to apply an "open sink-fold" .
20.The crease patter of "open sink-fold" of the step #19 is shown here.