US surgeons have transplanted a genetically modified pig's heart into a human in a historic event.
David Bennett, a 57-year-old handyman, is doing well after the nine hour operation last Friday and has shown no signs of rejecting the organ.
Bennett has a life-threatening condition and said the transplant was a 'do or die' event as he was ineligible to get a human heart transplant.
Surgeons at Baltimore's University of Maryland Medical Centre granted permission to do the experimental surgery by America's regulating body, the Food and Drug Administration, on the grounds that Bennett would have otherwise died.
Speaking of the procedure, Dr Bartley Griffith, the director of the cardiac transplant programme at the centre and who conducted the operation, said: "It creates the pulse, it creates the pressure, it is his heart.
"It's working and it looks normal. We are thrilled, but we don’t know what tomorrow will bring us.
"This has never been done before."
Bennett agreed to be the first to risk the experimental surgery in December, hoping it would give him a new life.
"This is nothing short of a miracle," his son David Jr said.
"That's what my dad needed and that's what I feel like he got."
Doctors replaced his heart with one from a one-year-old, 17-stone pig gene-edited and bred specifically for this purpose.
Dr Griffith said he first mentioned the experimental treatment last month, saying it was a "memorable" and "pretty strange" conversation.
"I said, 'We can’t give you a human heart. You don't qualify. But maybe we can use one from an animal, a pig,” Dr Griffith recalled. "It's never been done before, but we think we can do it.'"
"I wasn't sure he was understanding me,” the doctor added. “Then he said, 'Well, will I oink?'"
So far, Bennett is breathing on his own without a ventilator, though he remains on an extracorporeal membrane oxygenation machine that is doing about half the work of pumping blood throughout his body.
Doctors plan to slowly wean him off.
Bennett decided to undergo the pioneering surgery on the experimental treatment because he would have died without a new heart, had exhausted other treatments and was too sick to qualify for a human donor heart, family members and doctors said.
"This is a watershed event," said Dr David Klassen, the chief medical officer of the United Network for Organ Sharing, who was formerly a transplant surgeon at the University of Maryland.
"Doors are starting to open that will lead, I believe, to major changes in how we treat organ failure."
Pigs have similar organs to humans and scientists have been working for decades to discover how to save human lives with animal organs.
