<Tr> <Th> Significant other (s) </Th> <Td> Callie Torres </Td> </Tr> <P> Erica Hahn, M.D. is a fictional character from the American Broadcasting Company (ABC) medical drama television series Grey's Anatomy, portrayed by actress Brooke Smith . Hahn was a recurring character through the show's second and third seasons, and joined the main cast in the fourth season . Prior to assuming the role, Smith observed heart surgery being performed, and admitted to finding stressful the pressure of continually portraying a medical professional realistically . </P> <P> The character is presented as highly professional, to the point of being a "workaholic". She is notably hard on Resident Cristina Yang (Sandra Oh), admitting that Cristina reminds her of herself as a student . Despite her intentions to keep away from relationships, she becomes romantically involved with orthopedic surgeon Callie Torres (Sara Ramirez). The storyline was praised for its realistic portrayal of a developing same - sex relationship between two women, although consultants from the Gay & Lesbian Alliance Against Defamation expressed some concerns over what they deemed the somewhat exploitative talk of a threesome between Hahn, Torres and Mark Sloan . Hahn was written out of Grey's Anatomy in November 2008, with Smith commenting that the decision originated with the ABC network rather than with series creator Shonda Rhimes . </P> <P> Upon her first appearance in the series it is established that Hahn is a long - time rival of main character and fellow cardiothoracic surgeon Preston Burke, dating back to their days at Johns Hopkins University School of Medicine, where she graduated second after Burke . She is introduced as a cardiothoracic attending surgeon at Seattle Presbyterian Hospital when she and Burke fight over a donor heart . Hahn reappears in season three when she is contacted by George O'Malley (T.R. Knight) for a consult on his father's valve replacement after George finds out about Burke's hand tremors and Cristina helping him cover it up . Hahn transfers to Seattle Grace Hospital in the season four episode, "Haunt You Everyday", after performing a successful heart transplant at the request of the Chief of Surgery, Richard Webber . She takes on the role previously held by Burke, Seattle Grace's Head of Cardiothoracic Surgery . Hahn cultivates an antagonistic relationship with Burke's former protégée Cristina Yang, refusing to let her scrub in on surgeries, and constantly criticizing her overly enthusiastic behavior . She later confesses to Addison Montgomery (Kate Walsh) that she is purposely hard on Cristina, as she reminds her of herself as a Resident . </P>

When does dr. hahn leave grey's anatomy