O'Rourke was on a trip to a California movie studio when she was discovered by Steven Spielberg outside a cafeteria. Spielberg was looking for someone to fill in the role of 5 year old "Carol Anne" in his upcoming production of Poltergeist. He thought O'Rourke looked just perfect for the part, so he gave her a reading which she passed.
O'Rourke then filmed Poltergeist, released in 1982, and her phrase "They're He-eere!" entered American pop culture.
In 1986, Poltergeist II was released, and once again, O'Rourke coined another pop-culture phrase, when she said "They're ba-aaack!"
O'Rourke filmed Poltergeist III in 1987, and the movie was set to be released in 1988.
Unfortunately, O'Rourke never got to see Poltergeist III. In February of 1988, a few months before the movie's release, Heather's life was cut short by complications from a congenital bowel obstruction. She died at a hospital in San Diego.