“The human heart is not shaped like a valentine heart, perfect and regular in contour, it is slightly irregular in shape as if a small piece of it were missing out of its side. The missing part may very well symbolize a piece that a spear tore out of the universal heart of humanity on the Cross, but it probably symbolizes something more.
It may very well mean that when God created each human heart, he kept a small sample of it in heaven, and sent the rest of it into the world, where it would each day learn the lesson that it could never be really happy, that it could never be really wholly in love, that it could never be really whole-hearted until it rested with the Risen Christ in an eternal Easter.”

~ Archbishop Fulton Sheen (Manifestations of Christ)