To beat the game of Zelda with only the three hearts you have at the beginning. This means not picking up any of the heart pieces at the end of each temple and not doing any other thing that would gain you heart pieces throughout the game.
"I pretty much owned The 3 Heart Challenge. I must say... not picking up that first heart piece was truly a test of will-power... knowing that I would have to fight Ganon with only 3 hearts!"
by Brett Goodman December 11, 2006