Heart Scales are used to teach your Pokemon moves you forgot or never learned at the Move Relearner in Dendemille Town. To get Heart Scales in Pokemon X and Y, you need the Old Rod from Ambrett Town in the Aquarium by the Magikarp Statue, and TM46 (Thief) from Cassius's house in Camphier Town. Use the Old Rod on Route 8 - Muraille Coast to battle Luvdiscs, which have a 50% chance of dropping a Heart Scale. Keep fishing for an infinite amount of Heart Scales. Note: Change spots if Luvdisc does not take the bait.