The pilot, Henry Skillern, 63, of Humble, was at the controls of United flight 1603 when he suffered the attack. The Boeing 737-900, which was carrying 161 passengers and a crew of six, made an emergency landing just before 8pm on Thursday in Boise, Idaho.
Audio from LiveATC.net was released: "United: We got a man down, chest compressions going on right now. I'm not sure too much right now the status."
Skillern was still alive when he arrived at Saint Alphonsus Regional Medical Center but died overnight while undergoing treatment, spokeswoman Jennifer Krajnik said Friday.
"Somebody who could see said that they saw someone giving the pilot CPR and we were on the ground about 20 minutes later," said passenger Scott Hyed.
"I just saw them working on the captain. I didn't see much other than that, but they were working on the captain," said passenger Bryant Migill.
Passengers were put on another plane that landed at Sea-Tac Airport just after midnight.
One man tweeted, 'Kudos to United for its professional manner.'
The pilot's family has been notified of his passing.
The Associated Press contributed to this report
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