Arnold Schwarzenegger jokes 'I'm back' in first tweet since undergoing heart surgery

Arnold Schwarzenegger has tweeted for the first time since undergoing heart surgery, telling fans: "I'm back."

The 70-year-old Terminator actor and former California governor underwent a scheduled procedure to replace a valve on Thursday.

On Monday he told his 4.43 million followers on Twitter: "It's true: I'm back!

He thanked doctors and nurses at the Los Angeles hospital and said he is "truly filled with gratitude" for messages received from fans since the operation.

His spokesman Daniel Ketchell said last week that an open-heart surgery team was prepared in case the scheduled procedure could not be performed "as they frequently are in these circumstances".

Mr Schwarzenegger wrote on the social network: "I went to sleep expecting to wake up with a small incision and woke up with a big one - but guess what? I woke up, and that's something to be thankful for.

"Thank you to the doctors and nurses. And I'm truly filled with gratitude for all of the kind messages."

The pulmonic valve originally was installed in 1997 for a congenital heart defect and had to be replaced.

The Hollywood star was an award-winning bodybuilder before becoming an actor and politician.

He served as governor of California from 2003 to 2011.