For this cheat you will need a copy of CAPTIVE. Load the game as per usual. On the level selection screen, insert your Captive disc. Press Fire and the screen will say "Disk Error". Now replace your Captain Planet disc and the cheat will be active.
Complete the fire level and get killed on the water level. Now on the high score table, enter "BBBB" for your name. This will give you infinite continues.
Run through the game as normal until you get to the level selection page. Now type in "GO PLANET". Now, when the game starts hit 'F10' and 'RETURN' together, and you should be taken back to the level selection page, where you can choose any level.
On the Heart level, after climbing the trees and killing the beasties, you will be ready to enter the Eco-Copter. Next to the Eco-Copter, you will see a tunnel going down to where you just came from. Go down the tunnel and manoeuvre your way to the bottom (avoiding the trees on the way). You will then find a bird. Land on its back and you will gain 5000 points and an extra life.
On the fifth level, first of all you have to get rid of all the toxic cans. When you get to the Eco-Copter, follow the slope (where the boulders have been rolled) until you find some pit-ponies. Take them up to where you came out and drop them into the field. This should get you much closer to the end of the level.