Heart-shaped books, like this one from France in the 1400s, were common during the Middle Ages. Hearts were important metaphors for religious love within Christianity and eventually love in a non-religious sense. They also had ties to memory, the soul, and more!

This book is the Chansonnier cordiforme de Montchenu, 1470–80, Collection Henri de Rothschild MS 2973, held in the Bibliothèque Nationale, Paris, France.