Arnold Schwarzenegger admits he's still not feeling ''great'' after recently undergoing open-heart surgery.

The 70-year-old actor - who also served as the Governor of California from 2003 until 2011 - has provided an update on his health in a video posted on his Twitter account, and Schwarzenegger has also thanked his fans for their support since he went under the knife last month.

He said: ''Thank you so much for all your wishes and for all the cards and the phone calls and the emails and the texts and all this kind of stuff that I got from around the world.

''I really appreciate that very much and you're very kind.''

Initially, Schwarzenegger's operation was just intended to replace a valve being used to correct a congenital heart defect - but he ended up having open-heart surgery.

And while the Hollywood star has revealed he is making a good recovery, Schwarzenegger still remains some way off being back to full health.

He shared: ''I just wanted you to know that I'm feeling much better. I can't say - even with my positive attitude - that I'm great, because I'm not great yet.

''Great is a totally different level. But I'm good. I feel good.''

News of Schwarzenegger's operation was first revealed by his spokesperson, Daniel Ketchell, in March.

In a statement, he explained: ''That 1997 replacement valve was never meant to be permanent, and has outlived its life expectancy, so he chose to replace it yesterday through a less-invasive catheter valve replacement.

''During that a procedure, an open-heart surgery team was prepared, as they frequently are in these circumstances, in case the catheter procedure was unable to be performed. Governor Schwarzenegger's pulmonic valve was successfully replaced.''