Terminator star, Arnold Schwarzenegger, has undergone emergency open-heart surgery, according to US reports.

The 70-year-old underwent the medical procedure on Thursday, according to TMZ.

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 Schwarzenegger was in theatre for several hours.

The former governor of California is believed to be in a stable condition.