The 57-year-old comedian returned to TV on Wednesday night's episode of The Late Show with David Letterman, eight weeks after he underwent surgery at a Cleveland clinic to replace an aortic valve.
The funnyman thanked the doctors who saved his life as he showed pictures of his chest scars on the show, and admitted doctors had warned him he'd die if he didn't go under the knife.
He said, "They gave me... they said two weeks. I mean, when they initially went in, there was one doctor who I found out was going on vacation the next day who wanted to do the surgery that day.
"(Another) doctor said, 'Maybe you want to wait. You never want to have a surgery with a guy who wants to go someplace'... But they said two weeks, and that allowed me to make the decisions... You want to look for someone who's done a lot of them."
But Williams is in still high spirits, after postponing the rest of his comedy tour until September, when he'll return to the stage in Indiana.
Joking about his new body parts, he adds, "I have one new valve and a repaired valve. I have a cow valve, which is great, and the grazing's been fun."
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