Since anyone reading this has probably come here looking for origami, it seems like a good idea to start off with something you can actually fold. It’s a recent design that began as a doodle from an odd leftover scrap of paper, but then I worked out how long the strip needed to be and managed to find a convenient way to get it from a standard sheet of A4.
Heart by Edwin Corrie
I like to class this sort of thing as an “oddity”, because it doesn’t start from a square and is not as refined and elegant as many of the more classical origami heart designs. But it somehow works out in a satisfying and interesting sort of way. I’m sure it could be improved and made neater and more regular, so if you like the idea please feel free to have a go.
Let’s face it, if you want a good origami heart there are plenty out there to choose from. For example, here’s a nice collection called Origami With Love from Nick Robinson that you might want to check out. Available from his website at https://nickorigami.com/product-category/books/.
Origami With Love by Nick Robinson
I folded the model following the instructions from A4. After a little math, it looks to me like the starter strip has a proportion of around 1 x 3.5 (3.569 to be more exact). And your cutting from A4 allows for preparatory 1/5 and 3/5 folds.
But starting directly from a 1 x 3.5 (1/4 square minus 1/8) it is not difficult to obtain these folds "by eye" ...
The final model can be used as a corner bookmark: the large half-trapezoid is slipped into the corner and the small half-trapezoid will protrude from the page when the book is closed