The Legend of Zelda: Oracle of Seasons/Heart Pieces

There are 12 Heart Pieces to be found. Every four pieces make an extra Heart Container, for a total of three.

Heart piece in Horon Village

 * Earliest availability: chapter 2, Horon village
 * Requirements: seed satchel and ember seeds (found in the 1st dungeon)

Hop down the ledge just south of the mayor's house, go up the steps, and burn down the small tree with an ember seed to get your heart piece.

Heart piece in east suburbs

 * Earliest availability: chapter 2, East suburbs
 * Requirements: Rod of Seasons & Power of Winter

Go out the eastern exit of Horon Village (south of the Woods of Winter) and then head east one more screen. Hop on top of the stump and change the season to winter. Head north one screen and west one screen, and enter the cave. Inside is a heart piece.

Heart piece in Woods of Winter

 * Earliest availability: chapter 3, Woods of Winter
 * Requirements: power bracelet (found in the 2nd dungeon)

In the Woods of Winter, find the pond; lift the rock with the power bracelet and claim the heart piece.

Heart piece in Subrosian market

 * Earliest availability: chapter 3, Subrosian market
 * Requirements: 10 ember seeds and 10 ore chunks

Link can buy the heart piece in the market for the price of 10 ember seeds plus 10 ore chunks.

Heart piece from Maple

 * Requirements: nothing, but Pegasus Seeds and Maple's Ring are helpful
 * Earliest availability: chapter 3, anywhere after Link gets Pegasus seeds.

Maple appears after the next screen transition every time Link defeats 30 enemies (every 15 enemies, if he wears Maple's Ring). Occasionally, Maple will drop a heart piece if you hit her. She will prioritize it first, so use Pegasus seeds to get there faster than her. The heart piece appearance is completely random, so it may take a while to get.

Heart piece in Moblin's keep

 * Earliest availability: chapter 4, Moblin's Keep
 * Requirements: animal friend's flute

With the help of his animal friend, Link can reach the western entrance of the Great Moblin's keep. After defeating him, a chest holding the heart piece can be found in the ruins.

Heart piece from a Gasha nut

 * Earliest availability: chapter 4, Goron Mountain
 * Requirements: shovel

There are four Gasha spots where one Heart Piece can be obtained:
 * 1) Goron Mountain base (accessible from chapter 4)
 * 2) Eyeglass Lake, near Unicorn's Cave (accessible from chapter 5)
 * 3) Mount Cucco, in autumn (accessible after chapter 5)
 * 4) Tarm ruins (accessible from chapter 6)

Heart piece on Mount Cucco

 * Earliest availability: chapter 4, Mount Cucco
 * Requirements: power of Spring

On Mount Cucco, change the season to spring. Then, use a "spring flower" to be thrown on an upper ledge. Go east a few screens, then jump down near the tree stump.

Heart piece in Spool Swamp

 * Earliest availability: chapter 4, Spool Swamp
 * Requirements: power of Spring and Zora flippers

Go to the tree stump near the entrance of Poison Moth Lair (dungeon 3), and switch the season to spring. Follow the river all the way south, and the current will bring Link to this heart piece.

Heart piece in Eyeglass Lake

 * Earliest availability: chapter 5, Eyeglass Lake
 * Requirements: Zora flippers and power of Summer

In the Eyeglass Lake area, switch the season to summer, swim through a small stretch of water, then explore the eastern basin. Lift a rock and explore the mini-dungeon (three rooms) to get the heart piece from a chest.

Heart piece in the graveyard

 * Earliest availability: chapter 8, graveyard
 * Requirements: power of Autumn and Roc's cape

After clearing the seventh dungeon, get to the tree stump on the west coast. Using the Roc's cape, go back to the graveyard and collect the heart piece using the power bracelet.

Heart piece in the temple remains

 * Earliest availability: chapter 8, temple remains
 * Requirements: bombs and Roc's cape

After Link made the Subrosian volcanoes erupt (using a bomb), this room becomes accessible. Blast the entrance with a bomb, then use the roc's Cape to reach the heart piece.