David Bennett, 57, died Tuesday at the University of Maryland Medical Center. Doctors didn’t give an exact cause of death, saying only that his condition had begun deteriorating several days earlier.

Bennett's son praised the hospital for offering the last-ditch experiment, saying the family hoped it would help further efforts to end the organ shortage.

“We are grateful for every innovative moment, every crazy dream, every sleepless night that went into this historic effort,” David Bennett Jr. said in a statement released by the University of Maryland School of Medicine. “We hope this story can be the beginning of hope and not the end.”

Doctors for decades have sought to one day use animal organs for life-saving transplants. Bennett, a handyman from Hagerstown, Maryland, was a candidate for this newest attempt only because he otherwise faced certain death — ineligible for a human heart transplant, bedridden and on life support, and out of other options.

After the Jan. 7 operation, Bennett's son told The Associated Press his father knew there was no guarantee it would work.