This video has all the locations of every heart piece in The Legend of Zelda: Link's Awakening. Read the description for more indepth information.

Heart Piece #1 (0:00):
Found in Mabe Village. Cut down a bush and fall down the well to get this first heart piece.

Heart Piece #2 (0:17):
Fisherman in Mabe Village. Do some fishing and reel in the big fish near Link to get this heart piece.

Heart Piece #3 (1:22):
Found in Koholint Prairie. Pretty much unmissable. Use your Roc's Feather to nab this one.

Heart Piece #4 (1:34):
Found in Mysterious Woods. Use the Power Bracelet to lift up the skull blocking this heart piece.

Heart Piece #5 (1:57):
Found in Graveyard. Near the lone grave is a pair of stairs that leads into a cave. Jump the gaps and move a rock to be able to jump to this heart piece.

Heart Piece #6 (2:21):
Found in Ukuku Prairie. After you beat Key Cavern, use the Pegasus Boots to destroy the rocks and then bomb a wall near the top of this cave to find this heart piece.

Heart Piece #7 (2:51):
Found in Yarna Desert. Walk into the cave or fall down the quicksand to end up in the room right below the heart piece that is behind another bombable wall.

Heart Piece #8 (3:14):
Found under Tal Tal Heights. At the bottom of the heights is a cave full of water. Under water where you would normally fall from an area up above is a hidden heart piece.

Heart Piece #9 (3:44):
Found near Kanalet Castle. Much like the previous heart piece, this one is under water, but takes fooooorever to get to. Keep swimming and dive under a very random spot for this heart piece.

Heart Piece #10 (4:22):
Found in Animal Village. After you beat Catfish's Maw, head back to Animal Village to this bombable cave. Jump the gaps and then use the Bow & Arrow + Bomb combination to destroy the cracked boulders across the chasm and then use the Hookshot to get across to this heart piece.

Heart Piece #11 (4:53):
Found in Tal Tal Mountains. Cross the wooden bridge towards a pair of stairs that leads into a cave. Bomb a wall down below and then head one screen over for this heart piece that taunted us a long time ago.

Heart Piece #12 (5:31):
Found in Turtle Rock. After you progress enough into this dungeon, a pair of stairs will lead back to the outside world with the final heart piece resting on top of a small mountain.