It is believed that the heart shape originated from the city-state Cyrene. During the 7th century B.C., this area was known for the rare North African plant silphium. The seedpod of this plant is the shape of the heart that we know today.
Sometimes used for birth control, silphium was first associated with sex and later became a symbol of love. This plant was so important to the economy of Cyrene that it was minted on their currency.
The Catholic Church states that the modern heart shape originated with a story of Saint Mary Margaret Alocoque, who had a vision of a heart surrounded by thorns. This symbol became known as the Sacred Heart of Jesus.