The Best, Most Nostalgic Part of Grey's Anatomy's 300th Episode Is the Music

In the 300th episode, it's only a cover, but it's still pretty unmistakable. "Keep Breathing" plays during a surgery sequence near the end of the episode. But this song also plays at one of the most heartbreaking moments in the show! In the season three finale, Burke leaves Cristina at the altar. The song plays as Cristina marches around the apartment in her wedding dress, realizing that all of his things are gone. She starts to break down and hyperventilate, and Meredith cuts her out of her wedding dress.