The 3 Hearts are three highly powerful artifacts supposedly created by Calypso and given to the three races that govern the Sea: Humans, Merfolk, and Atlanteans. They consist of the Trident, an immensely powerful weapon that goverened the waves and weather; the Heart of Atlantis, a sentient crystal which brought life to those it was bound to, and the Flying Dutchman, which ferried the dead that died at sea.
According to legend, he/she who possesses these three would become a god of the Seas.