The 70-year-old underwent the medical procedure on Thursday, according to TMZ.
Mr Schwarzenegger was scheduled to have a catheter valve replacement and developed complications, US reports say.
The procedure usually means the patient can avoid having open-heart surgery.
Doctors at Cedars-Sinai hospital in LA reportedly decided an emergency open-heart operation was needed and the operation lasted several hours.
The former governor of California is believed to be in a stable condition.
The action star is due to reprise his previous roles as robot killer The Terminator and Conan the Barbarian over the next two years.
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This is not the actor’s first heart operation. In 1997, Mr Schwarzenegger underwent elective heart surgery to replace a heart valve.