Last week, a 57-year-old man underwent the first successful transplant of a pig heart into a human body, the University of Maryland announced Monday.

The patient, David Bennett, was not eligible for a conventional heart transplant, due to heart failure and an irregular heartbeat. Prior to the surgery, he spent six weeks in the hospital, and was connected to a heart-lung bypass machine. The Food and Drug Administration gave emergency authorization for the experimental surgery on Dec. 31. 

Over the last five years, Dr. Bartley Griffith and Dr. Muhammad M. Mohiuddin have been working on perfecting techniques for transplanting pig hearts into non-human recipients, NBC News reports. The pig hearts have been genetically modified with a sugar removed from its cells, lowering the chance of rejection.

In a statement, Griffith called Bennett’s surgery a “breakthrough.” There are “simply not enough donor human hearts available to meet the long list of potential recipients,” he added. “We are proceeding cautiously, but we are also optimistic that this first-in-the-world surgery will provide an important new option for patients in the future.” The FDA says that every day, 10 people die in the United States while waiting for a donated organ.

Bennett will be monitored for the next several weeks, and appears to be doing well. The University of Maryland said that prior to the surgery, Bennett declared, “It was either die or do this transplant. I want to live.”