Armstrong, who turned 82 on Sunday, underwent surgery on Tuesday to relieve blocked coronary arteries. NBC news quoted his wife Carol Armstrong as saying he is "doing great."

As commander of the Apollo 11 mission, Armstrong became the first human to set foot on the moon on July 20, 1969. After piloting the module Eagle to the moon, he climbed down the stairs onto the dusty surface and said: "“That's one small step for a man, one giant leap for mankind."

NASA Administrator Charles Bolden called Armstrong a "true American hero" and wished him a quick recovery.

"Neil's pioneering spirit will surely serve him well in this challenging time and the entire NASA family is holding the Armstrong family in our thoughts and prayers," Bolden said in a statement.

Armstrong flew combat missions during the Korean War and was a test pilot for a U.S. aeronautics agency that would become NASA. After leaving the space agency, he taught at the University of Cincinnati in his home state of Ohio.

He and his wife live in the Cincinnati area.

(Reporting by Jane Sutton)

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