James Pickens, Jr. acted as Seattle Grace Hospital's Chief of Surgery, Richard Webber, who has to deal with the choice between his career and his marriage. Kate Walsh played Addison Montgomery, obstetrician-gynecologist and neonatal surgeon, who comes to terms with her husband Derek Shepherd's desire to divorce, while dealing with the arrival of her former lover. Isaiah Washington played the role of attending physician and cardiothoracic surgeon, Preston Burke, who becomes engaged to intern Cristina Yang after their developing a relationship. Patrick Dempsey portrayed attending neurosurgeon Derek Shepherd, whose relationship with intern Meredith Grey has been the focal-point of the series since its inception. Sara Ramirez began receiving star-billing in the season premiere, after numerous appearances during the last episodes of the second season. She portrayed orthopedic surgeon and fifth-year resident, Calliope "Callie" Torres, whose relationship with intern George O'Malley evolves into a sudden marriage with unpleasant repercussions. Eric Dane was also promoted to the series regular status after a guest appearance in the eighteenth episode of the previous season, and an uncredited one in the second episode of this season. He began receiving star-billing in the third episode of the season, portraying attending physician, otolaryngologist and plastic surgeon Mark Sloan, whose arc, describing the attempt at resuming his relationship with Addison Montgomery, is heavily developed throughout the season.
