The 30-year-old actor has starred in the films "Black Hawk Down," "Blow Dry," "Pearl Harbor," "Sin City" and "Lucky Number Slevin."
People.com quoted Hartnett's publicist, Susan Patricola, as saying the film star had been staying at the Chateau Marmont in West Hollywood when he fell ill early Monday morning and was transported to the hospital via ambulance.
Patricola emphasized Hartnett was able to walk on his own at the time and said the illness was a "flare-up" of an ongoing gastrointestinal problem he has been dealing with for the last several months, People.com said.
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