The Legend of Zelda: Link's Awakening/Sidequests/Heart Pieces

Heart Piece 1
Any time after you've got your sword, slash the bushes and fall down the Mabe Village well for a Piece of Heart.
 * Item needed: Sword

Heart Piece 2
Head into the first Mysterious Forest cave, the one on the way to the toadstool, to find this piece.
 * Item needed: L-1 Bracelet

Heart Piece 3
After getting the Roc's Feather, jump onto this platform to claim your third Piece of Heart.
 * Item needed: Roc's Feather

Heart Piece 4
North from Bow Wow's house you can talk to a man and play the fishing minigame. Catch the large fish closest to you for a heart piece. You may have to clear out the other fish first by catching them too, so bring plenty of Rupees.