The heart pieces are numbered by the order in which they were discovered to be distinct heart pieces.
The first extra heart piece is located in the child scene setup for Gerudo Fortress, positioned on top of the platform area above the prison. Of all the extra heart pieces, this is the only one that can be obtained in the 64 version.
To reach this heart piece, you must use Death Hole Wrong Warping in combination with Ocarina Items (or Ocarina on B if applicable).
As Young Link, use up any fairies that you may have and deplete your life to a low level. Next, place a Farore's Wind warp point inside the Thieves' Hideout room that leads to the top of the prison via a barricaded slope (of which is normally crossed by using the hookshot on the rafters above). Equip bombs and a cinematic item (other than Farore's Wind) to the X/Y buttons and perform Death Hole. Restore menu functionality through Ocarina Items, equip bombs and Farore's Wind to the X/Y buttons, and warp back to the point. Kill yourself with bombs so that you can select Continue from the Game Over screen. Although you'll respawn beyond the wooden barricade at the room's exit, avoid heading outside since the game will "Blackscreen" because of the cutscene in the area.
Instead, place a new Farore's Wind point and then warp to Hyrule Castle by playing Bolero of Fire via Ocarina Items. Get caught by the guards to easily restore normal game/menu functioning and return to the previously set warp point. Leave the room and collect the heart piece.
The next extra heart piece is located in cutscene setups 0 and 1 for Kakariko Graveyard, inside of a chest very close to where you normally obtain the heart piece up on the ledge.
You can obtain this heart piece through Death Hole Wrong Warping. Set Farore's Wind at the main entrance to Kakariko Graveyard, perform Death Hole, then use the hookshot to reach the heart piece.
This heart piece is in cutscene setup 0 for Jabu Jabu's Belly, also known as "Glitched" Jabu Jabu. From the room that branches out into 5 different doors, it's the second door from the right.
To be able to obtain this heart piece, you cannot have opened the compass chest, because the heart piece chest shares the same permanent flag as the compass chest. Complete the dungeon enough so that you can set a Farore's Wind point in the proper room. Then perform Death Hole Wrong Warping and return to your Farore's Wind point.
This last known distinct heart piece is located in cutscene setups 4 and 5 for Kokiri Forest, positioned atop the Kokiri Shop. However, this heart piece behaves differently than normal heart pieces because it doesn't set it's perm flag value properly. Because of this the heart piece will suddenly appear over Link's head once you walk close enough for it to load, as if it were a normal bomb drop or similar, and the heart count won't increase.
It is currently impossible to reach this heart piece.
After finding the random heart piece from playing Dampe's Graveyard Game as a child, the heart piece resets to another random spot as if the minigame was never won, and can be found again by continuous attempts. As long as you have rupees, you can continue to play Dampe's Graveyard Game and dig up an infinite amount of heart pieces. This lets you surpass the maximum of 20 hearts for each extra 4 pieces you dig up, and the display for each additional heart after 20 is added when unlocked. Each of these hearts is displayed in the very most upper-left of the touch screen and lay on top of the extra heart icon before it. The 21st heart is a small, partially transparent black circle. The 22nd heart is a circle of identical size with the same stone texture as the “VIEW”, ocarina, “I”, and “II” touch buttons. The 23rd heart is a yellow uppercase letter “B”. The 24th heart and on are invisible for what has been seen so far. Except for the invisible hearts, the extra heart icons blink in size the same way as regular hearts when it is the current heart of health. The extra heart icons do not change at all when damage is taken until the whole heart is gone, and then they just stop blinking and remain laid on top of the extra heart icon before it. On initial loading of a file, the extra heart icons are invisible until they are in the blinking state. However, once in the blinking state, the extra heart icon remains on the touch screen combat menu until the game application is completely restarted, even if a different file is loaded. This is simply an aesthetic error and does not change how your hearts behave normally in other files.