It’s the first time a pig’s heart has been successfully transplanted into a human being. According to surgeons at the University of Maryland Medical Center, the eight-hour procedure took place in Baltimore on Friday, and the patient, David Bennett Sr. of Maryland, was doing well on Monday. A 57-year-old man with life-threatening cardiac illness has gotten a heart transplant from a genetically engineered pig, a pioneering technique that provides hope to hundreds of thousands of patients whose organs are failing.

Scientists have been working hard for the past decade to create pigs whose organs would not be rejected by the human body, with new genome editing and cloning technology accelerating the study. The heart transplant comes only months after doctors in New York successfully transplanted a brain-dead person’s kidney from a genetically modified pig.

Researchers believe that surgeries like this may usher in a new age in medicine in the future, when replacement organs are no longer in short supply for the more than 500,000 Americans waiting for kidneys and other organs.

According to family members and physicians, Mr. Bennett chose the experimental procedure because he would have perished without a new heart, he had exhausted all options, and he was too ill to qualify for a human donor heart.

His doctors indicated he may be removed off the machine on Tuesday since his new heart is working and handling most of the job. Mr. Bennett is being constantly examined for signals that his body is rejecting the replacement kidney, but the vital first 48 hours went off without a hitch.

He’ll also be checked for illnesses, such as porcine retrovirus, a pig virus that may be transferred to humans, though the risk is minimal.