"Shiny Happy People," the 22nd episode of Grey's Anatomy season six, explores themes of long-term love and medical advocacy, featuring a guest performance by Demi Lovato. The plot centers on Alex Karev diagnosing a young girl's heart condition and the staff navigating complex romantic developments, such as the reunion of an elderly couple and Mark Sloan's confession of love to Lexie Grey. For a full summary, see the Wikipedia entry for the episode .