Fold the card stock paper in half. Draw two vertical lines from the edge of the folded part, at a distance of 2 inches. The length of the lines should be around one inch. The greater the length, the greater the pop up effect but do not draw a line more than half of the card width, else it will show from the other side.
Image courtesy: makeandtakes.com
Cut along these lines using the scissor.
Fold up the cuts you made so that they make a flap like in the picture. Fold on the crease to make out the firm shape.
Draw a heart on the second piece of paper. The paper can be of red color or you can color or paint it red. Personalize it with a message, photos or anything you want to add on.
Image courtesy: alphamom.com
Fold this heart in half. Use a paper glue to stick it to the front of the flap (not top) so that it pops out whenever you open up the card.
Since the outside of the card will have cut lines which will give rough look, take a larger piece of paper. Fold it in half along the crease of the card and paste it to the outside of the card so that it covers the cuts you made.