Braving frightful dungeons filled with devious traps and wicked monsters is a risky business, and Link’s adventure can come to an end at any moment. Each time an enemy or a hazard hits Link, he takes damage and loses some of his life energy. The hearts that appear at the top of the Touch Screen show Link’s current life energy. If Link runs out of life energy (Hearts), he falls in battle and must begin from his last save point.
Of course, the game also ends if you fail to rewind time before the moon crashes down. This tragic fate is easily avoided once you reclaim the Ocarina of Time from the Skull Kid, though. Once Link has that magical instrument back in his possession, he can play the Song of Time and rewind back to the Dawn of the First Day at any moment.