In the nine-hour surgery, doctors replaced his heart with one from a 1-year-old, 240-pound pig gene-edited and bred specifically for this purpose.

So far, Bennett is breathing on his own without a ventilator, though he remains on an ECMO machine that is doing about half the work of pumping blood throughout his body. Doctors plan to slowly wean him off.

Scientists have been working for decades to figure out how to save human lives with animal organs. Right now, more than 100,000 people sit on organ transplant waitlists, suffering terrible symptoms and side effects. About 6,000 of them die every year waiting in vain for someone else’s tragedy to provide them with a new kidney, heart or lung.

Pigs have similar organs to humans. If those organs could be used in transplants, the waiting would end.