it does say "needle to the heart" in the song lyrics, but songs have to trim the words to fit the beat and melody of the tune. "like a knife to the heart" is the full correct idiom/expression. It means like a knife to the heart it will kill you. It is often used in the full version "like a knife to the heart" in songs to convey the feeling of somebody being painful hurt emotional and traumatically hurt. So it is not implying actual death but severe heart wrenching emotional pain distress grief and turmoil.

Christian, I have heard "like a knife to the heart" but not "needle to the heart."