Arnold Schwarzenegger speaks after heart surgery: "I'm back!"

LOS ANGELES -- Arnold Schwarzenegger made his first public comments since undergoing heart surgery to replace a valve last week. "It's true: I'm back!" the 70-year-old former governor tweeted on Monday.

"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," Schwarzenegger added, thanking the doctors and nurses involved in the procedure.

The pulmonic valve originally was installed in 1997 for a congenital heart defect and had to be replaced. Doctors originally planned to replace the valve via a less invasive catheter procedure, Schwarzenegger's spokesman Daniel Ketchell said Friday. When the catheter procedure was unsuccessful, a team of doctors performed open-heart surgery to replace the valve.  

Schwarzenegger had a motorcycle crash that left him with several broken ribs in 2001. He had a hip replaced and rotator cuff surgery in 2003. He broke his right femur in a skiing accident in 2006.

The pulmonic valve replacement surgery was scheduled as his old one grew less effective.

"It was starting to not really be heavily symptomatic, but he'd get a little tired in the afternoon; but that was it. It wasn't at the point where the doctors said it's time now. But it was at the point where with his schedule, it made sense," Ketchell told CBS News chief medical correspondent Dr. Jon LaPook ahead of the procedure.