The design for this puzzle is well over one hundred years old. An example called United Hearts can be found in Professor Hoffmann's Puzzles Old & New, 1893.
A basic design element in this puzzle is the heart with the deep notch. The loop formed by the deep notch will fit through the eye in the other piece far enough to allow it to fit over the end of the protruding eye. This design is well over one hundred years old. See Double Bypass and Sweetheart for other examples of this basic design element.