Andy Russick was on a flight to Phoenix late Tuesday when a man rushed up from the back of the plane and put a baby boy down next him.
The infant apparently had had a seizure, and the man was trying to save his life, Russick said. The medical emergency prompted the pilot on US Airways flight 678 to make an emergency landing.
"The baby wasn't breathing when it came by me," Russick told CNN affiliate KIVK.
Then a man seated near Russick climbed over him to join the first man. He was a doctor, Russick said.
Together the two men worked on the baby, one of them performing what looked like CPR, Russick said.
When the baby let out a wail, one of the men cheered.
"He yelled something out like, 'a crying baby is a breathing baby,'" Russick said.
The plane, which had originated in Tampa, Florida, diverted to Houston for the medical emergency, said US Airways spokeswoman Liz Landau. It then continued on to Phoenix.
After the doctor sat back down, he told Russick that the baby had a very high fever, which may have had something to do with the attack.