57-year-old David Bennett received a heart like no other ... He was ineligible for a human transplant and, while doctors couldn't guarantee the transplant would work, the surgery was a matter of life or death, so he rolled the dice.

“It was either die or do this transplant. I want to live. I know it’s a shot in the dark, but it’s my last choice,” he said before undergoing the 7-hour surgery Friday at a Baltimore hospital.

The FDA had approved the operation for emergency use, since David had no other options.

Though it's still unclear if the transplant will actually take, he seems to be doing well days after the surgery... And, docs at the University of Maryland Medical Center say his transplant showed a heart from a genetically modified animal can work inside a human body without immediate rejection.

That's great news, because in the past such transplants failed because the patient's body would reject the animal organ. Now, Maryland surgeons used the heart from a pig that had received gene-editing ... to thwart rejection.