A 57-year-old man with life-threatening heart disease has received a heart from a genetically modified pig, a groundbreaking procedure that offers hope to hundreds of thousands of patients with failing organs.

It is the first successful transplant of a pig’s heart into a human being. The eight-hour operation took place in Baltimore on Friday, and the patient, David Bennett Sr. of Maryland, was doing well on Monday, according to surgeons at the University of Maryland Medical Center.

''It creates the pulse, it creates the pressure, it is his heart,'' said Dr. Bartley Griffith, the director of the cardiac transplant program at the medical center, who performed the operation.

''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.''