Surgeons at Children's Medical Center in Dallas operated on their youngest kidney transplant patient in two decades on Monday.
Doctors removed a kidney from 22-month-old Hayden Brazil's father, Adam, minutes before she received it.
Dr. Dev Desai said Hayden "is doing very well."
"We hope that this kidney will last 20-plus years," he said. "The average lifespan for a living donor kidney is about 18 years and, hopefully, this one will last much longer."
Hayden got sick right after she was born.
"Her eyes were swollen shut," said Jamie Brazil, her mother. "Her feet -- she couldn't wear socks. Her belly was hard, and every time I took her in, they said it was something normal."
Ultimately, Hayden was diagnosed with congenital nephrotic syndrome, a rare kidney disease that requires a transplant.
Jamie Brazil could not donate because her blood type is different than her daughters' type. Adam Brazil was the best possible match.
"I felt really blessed I was a match, because then she'd be on the waiting list for who knows how long," he said.
Adam Brazil, an Iraq War veteran who did two tours as a tank mechanic, is a man of few words. He said combat pales in comparison to this.
"Going to Iraq, it was more just missing family, missing my wife, missing my kids," he said. "There wasn't really any nerves."
But sending his daughter back for a kidney transplant was different, Brazil said. He said he would tell Hayden that he decided to give her a kidney, "because I love her."
His wife said she couldn't be more proud.
"He's fought for our country, and he's saving our daughter's life," she said.
"I don't think many people can do what he's done, and I don't know if many people would do what he has chosen to do, but I'm so blessed," Jamie Brazil said.
Hayden will likely remain in the intensive care unit for at least 48 hours and could go home in as few as two weeks.