Surgeon Muhammad M. Mohiuddin, MD leads a team placing a genetically-modified pig heart into a storage device at the Xenotransplant lab before its transplant on David Bennett, a 57-year-old patient with terminal heart disease, at University of Maryland Medical Center in Baltimore, Maryland, U.S. January 7, 2022. Picture taken January 7, 2022. University of Maryland School of Medicine (UMSOM)/Handout via Reuters

Dr. Bartley Griffith, head of the team at the University of Maryland Medicine who performed the operation, said Bennett, 57, is now off of the machine that kept blood circulating through his body for more than 45 days, including several days after the surgery. He is breathing on his own, and speaking in a quiet voice.

Griffith had planned to leave Bennett plugged into the heart-lung machine for another week or so — comparing it to "training wheels," as the pig heart got used to its new environment.

Bennett's son, David Bennett Jr., said his father can't wait to get out of the hospital and is grateful for the groundbreaking surgery.

Researchers, including physician-scientist Muhammad Mohiuddin of the University of Maryland School of Medicine, have been working for decades to develop pigs whose organs can be used to address global organ shortages. 

The heart transplanted into Mr. Bennett came from a genetically altered pig provided by Revivicor, a regenerative medicine company based in Virginia. The pig had 10 genetic modifications to make its organs more tolerable to the human immune system. A growth gene was also inactivated to prevent the pig’s heart from continuing to grow after it was implanted.