Because both the origins of Valentine's Day as a holiday and the use of the heart shape as a love symbol are unclear, it is difficult to know whether the shape has 'always' been a symbol for the holiday. There are a variety of theories about the origins of the heart symbol in connection with Valentine's Day. Some theories trace the origins of the symmetrical heart shape as a symbol for love to a heart-shaped leaf used for seasoning and birth control in the seventh century B.C.E., while other theories suggest that the heart shape is an incorrect rendering of the shape of the human heart.
Though there may have been earlier uses, the use of hearts in connection with Valentine's Day can be traced back at least as far as 17th century England, when the practice of exchanging written and decorated cards for the holiday became more popular. These were handmade and not commercially produced cards. Commercial valentines originated in America during the mid-1800s, and within about 50 years, images of Cupid and hearts were the popular iconography associated with this holiday.