23. What you need: nothing
Just before you actually get to the Southern Swamp area, there's a large black tree with bats all around. Climb the tree to get a piece of heart.
24. What you need: Clock Town Land TItle Deed
Give the Deku Scrub at the Tourist Info House in Southern Swamp the Land Title Deed you got in Clock Town to get the piece of heart on the roof of the house.
25. What you need: Pictograph Box
All you need to do is take a picture of the Deku King or Tingle and take the picture to the big guy at the Tourist Info House. He'll give you a piece of heart.
26. What you need: Hero's Bow
After you beat Odolwa at Woodfall Temple, go back to the Tourist Info House and talk to Kotake (or is it Koume?). Anyway, talk to her and play her game. Hit the target 20 or more times and she'll give you a piece of heart.
27. What you need: Deku Scrub Mask
In the area where the Woodfall Temple is, use the Deku Flowers to fly to a piece of heart on the right side of the area (from the owl statue, facing the temple).
28. What you need: Hero's Bow
Play at the Swamp Shooting Gallery and score over 2000 points to get a Quiver upgrade. Play again and get a perfect score to get a piece of heart.
29. What you need: Deku Mask
At the Deku Palace, make your way through the maze on the left. At the end, there's a piece of heart.