04/03/2009 at 07:00 PM EDT
Josh Hartnett has been released from L.A.'s Cedars-Sinai Medical Center, where he had been hospitalized since Monday for a gastrointestinal problem. "He's fine," his rep Susan Patricola tells PEOPLE. "They are running tests, which take time to get back and it's a process of elimination."
The 30-year-old Pearl Harbor
star was taken to the hospital
by ambulance Monday after complaining of abdominal pains. Patricola said Hartnett was under observation for a "flare-up" of gastrointestinal problem he has been suffering from for several months since starring in the London stage version of Rain Man
. "They just have to figure out what it is," she says.