Heart Scales are used to teach your Pokemon forgotten or never learned moves at the Move Relearner in Dendemille Town. Get the Old Rod from in the Aquarium by the Magikarp Statue in Ambrett Town and TM46 "Thief" from Cassius's house in Camphier Town Use the Old Rod on the Route 8 "Muraille Coast" to battle Luvdics for a 50% chance of getting a Heart Scale.