Fisher, 60, who played Princess Leia in Star Wars,
was taken ill on a flight from London to LA on Friday.
Passengers attempted to revive her with CPR
and she was taken to hospital when the plane landed.
Co-star Harrison Ford said he was "shocked and saddened" by the news.
"Our thoughts are with Carrie, her family and friends," he said.
Mark Hamill, who played Luke Skywalker, said he was sending "all our love"
and Peter Mayhew, who played Chewbacca, tweeted his thoughts
and prayers for "everyone's favourite princess".
Fisher's brother Todd said she was in intensive care in Los Angeles.
"We have to wait and be patient," he said. "We have so little information ourselves."
bbc news
Carrie Fisher in intensive care after suffering a heart attack
was taken ill on a flight from London to LA on Friday.
Passengers attempted to revive her with CPR
and she was taken to hospital when the plane landed.
Co-star Harrison Ford said he was "shocked and saddened" by the news.
"Our thoughts are with Carrie, her family and friends," he said.
Mark Hamill, who played Luke Skywalker, said he was sending "all our love"
and Peter Mayhew, who played Chewbacca, tweeted his thoughts
and prayers for "everyone's favourite princess".
Fisher's brother Todd said she was in intensive care in Los Angeles.
"We have to wait and be patient," he said. "We have so little information ourselves."
bbc news