The 57-year-old patient was a dead man walking.

“It was either die or do this transplant. I want to live. I know it's a shot in the dark, but it's my last choice,” said David Bennett, the patient, a day before the historic surgery would put a genetically-modified pig heart into his chest.

The groundbreaking procedure, performed by University of Maryland School of Medicine (UMSOM) faculty at the University of Maryland Medical Center (UMMC), was the only option left for the Maryland man after he had been “deemed ineligible for a conventional heart transplant” based on his medical records — at UMMC as well as a number of other leading transplant centers, according to a center statement.

The breakthrough transplant has shown, for the first time, that an animal heart can take the place of a human one without immediate rejection — the dominant risk in any transplant surgery.

The surgery is the next step in “solving the organ shortage crisis,” noted Dr. Bartley P. Griffith, who led the team that transplanted the pig heart into Bennett. Griffith, a transplant surgery professor at UMSOM and director of the Cardiac Transplant Program at UMMC, told the New York Times after the successful 8-hour surgery, “It creates the pulse, it creates the pressure, it is his heart,” adding, “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.”

The transplant is so cutting-edge that The U.S. Food and Drug Administration had to grant emergency compassionate use authorization for the procedure.

“The FDA used our data and data on the experimental pig to authorize the transplant in an end-stage heart disease patient who had no other treatment options," said UMSOM professor of surgery, Muhammad M. Mohiuddin, who established the Cardiac Xenotransplantation Program with Dr. Griffith, and also led the transplant team.

In addition to helping Bennett, the procedure yielded “valuable information to help the medical community improve this potentially lifesaving method in future patients,” he noted.

This new knowledge is critical because the present organ shortage is severe. Nearly 110,000 Americans are now awaiting a transplant, and over 6,000 patients die each year before they can have one of the lifesaving procedures.

The organ used in Bennett's transplant, dubbed a UHeart, came from United Therapeutics subsidiary Revivicor.

The successful surgery is “absolutely huge — for the patient, for the field, for Revivicor, for the transplant future,” Revivicor's executive vice president and chief scientific officer David Ayares said in a January 11 interview, according to The Business Journals.

Xenotransplantation — the use of non-human organs like the pig heart — could save thousands of lives if the dangers of rejection can be overcome.

To help fight rejection the UHeart experimental organ was modified in several ways. “Three genes — responsible for rapid antibody-mediated rejection of pig organs by humans — were "knocked out" in the donor pig. Six human genes responsible for immune acceptance of the pig heart were inserted into the genome. Lastly, one additional gene in the pig was knocked out to prevent excessive growth of the pig heart tissue, which totaled 10 unique gene edits made in the donor pig,” according to the UMMC report. In addition, Bennett was given conventional anti-rejection drugs, as well as a new experimental compound made by Kiniksa Pharmaceuticals.

This procedure and the development of the modified organ “has the potential to revolutionize the field of transplantation by eventually eliminating the organ shortage crisis,” stressed Dr. Christine Lau, the Dr. Robert W. Buxton professor and chair of the department of surgery at UMSOM and surgeon-in-chief at UMMC.