A U.S. man with terminal heart disease was implanted with a genetically modified pig heart in a first-of-its-kind surgery, and three days later the patient is doing well, his doctors reported on Monday.

The surgery, performed by a team at the University of Maryland Medicine, is among the first to demonstrate the feasibility of a pig-to-human heart transplant, a field made possible by new gene editing tools.

If proven successful, scientists hope pig organs could help alleviate shortages of donor organs.