Hollywood action star Arnold Schwarzenegger is in a stable condition after undergoing emergency open-heart surgery, his representatives said Friday, adding that his first words on waking were "I'm back."

The 70-year-old actor turned activist -- famous for the catchphrase "I'll be back" -- was in a Los Angeles hospital Thursday to have a valve replaced and developed complications, according to his spokesman Daniel Ketchell.

Doctors rushed the "Terminator" and "Predator" star into theater for open-heart surgery, operating for several hours, according to reports in the US entertainment press.

A hospital source confirmed that Schwarzenegger's first words when he woke up after surgery were, "I'm back," a play on his trademark film line.

He first used it in 1984's "The Terminator" and over the next 34 years repeated the phrase - or close variations -- in the sequels, as well as "Commando," "Raw Deal," "The Running Man," "Twins," "Total Recall," "Kindergarten Cop," "Last Action Hero," "Jingle All the Way," "The 6th Day" and "The Expendables II."