The first reported sighting of heart-shaped jewelry was somewhere near the finish of the Middle Ages. It was in the 15th and 16th Centuries, when it rose in popularity, and over time, found wide use in diamond jewelry.
The 20th Century story of King Edward VIII and Wallis Simpson involved the former presenting the latter with a Cartier-made heart charm. On opening it, you would see the an inscription which read ‘The Heart Has Its Reasons’, and when the king abdicated for the sake of love, the heart shape quickly came to represent true love.
The heart shape we are so familiar with was not there at the beginning. In original jewelry pieces, the shape was closer to pear, after which it evolved into a somewhat oval shape. This then developed into the heart shape that we all adore.