This is a png file for you to drag and drop to your desktop if you need help drawing hearts.
Start out with a page of hearts, however you make them is fine. They do not need to be folded in half, they do not need to be red, they do not need to be regular, they do not need to be symmetrical, they do not necessarily have to be hearts.
Drag and drop png file for V-mechanism.
If you must, a png file to help you crease a sheet of card stock in half. Otherwise just measure it.
Cut out the V-mechanism post, pre-crease along the dotted lines, align the point with the central fold and glue one of the two tabs.
Testing to make sure it closes properly, that nothing sticks out when it does close, that the alignment will work.
Then glue the other side in the folded position.
Close and weight down.
This is the way to assure both sides are perfectly even. But paper is not mathematical perfection of lines and points so sometimes the paper point is nicked off to eliminate the trouble of doubled card stock in tight places where paper thickness cannot be reduced to a mathematical point.
The hearts are glued to the structure and they can go right past it in all directions and cross over each other as these do where their planes intersect.
Each new heart added toward the edges is checked in the near-closed position before gluing to make sure it will not project past the edges when the card is closed. It's very important to check each addition until you see what is happening inside the card so that no heart is placed in interference with others and do not violate edge restrictions.
The little heart placed in the corner was glued, it is the heart on the right and this is how far it lifted up when the card is opened half way. Below you can see behind the large bright heart how far it moves when the card is fully opened.
Then hearts added with abandon and you can see how far you can go and in which directions, and which hearts can build out so that they connect forming a superstructure of its own around the original V mechanism which becomes more and more obscured with each additional heart. You can use hearts to disguise the structure. You have to decide for yourself when to stop adding hearts.
I want it to suggest an explosion so I'm adding lines to show that. We artist-types do that, change plans as we go and live with the results.
A few more hearts directly onto the background for the heck of it.
Think of some touching message of direct personal warmth. Honey, I love you so much I can't stand it sometimes, whenever I think of you my heart is aflutter.
You can use extra hearts for the cover, for the back of the card and for the envelope. Or stuff the card or envelope with them. Or keep them in your pocket.