Note: This code may longer work after the latest game update. Press Start to pause game play on Xbox Live when you are low on health. Rotate the D-pad in a full circle at least three times. Select the "Achievements" option at the menu. Press B to exit that screen. Select the "Resume Game" option. You will still remain at the same screen. Select "Resume Game" again. The game will begin with your character at full health.

Alternately, press Start to pause game play on Xbox Live when you are low on health. Press Xbox Logo to enter the Dashboard menu. Press Xbox Logo again to exit the menu, then resume the game.