– Dr. Leonard Bailey, a surgeon who opened new doors in medicine when he transplanted a baboon heart into an infant girl but then endured withering criticism for harvesting an organ from an animal to try to save the life of a human, has died of cancer. He was 76.

Bailey’s decision to transplant the baboon’s walnut-size heart into a 12-day-old infant known only as “Baby Fae” drew international attention and offered a possible future with an unlimited supply of animal organs to help save the lives of human patients.

But the moral and ethical questions of using animals as a virtual supermarket for hearts, livers and kidneys were so weighty that cross-species transplants failed to become the norm.

For Bailey, of Loma Linda, Calif., the 1984 surgery established him as a leading authority on heart transplants, a small-town doctor suddenly known internationally as a skilled and daring surgeon. But it all came at a price.

Criticized sharply by animal-rights activists who found the surgery to be ghoulish, Bailey was heckled when he spoke publicly. In 1985, Loma Linda officials suggested that he wear a bullet-resistant vest when he delivered a talk on the ethics of the Baby Fae operation. He canceled his talk instead.

Even Dr. Christiaan Barnard, the South Africa surgeon who rewrote the medical rule book with the world’s first heart transplant, wondered whether the Baby Fae transplant had gone too far.

“I used a baboon once, and then a chimpanzee and it was a traumatic emotional experience,” he said in a 1987 interview with the Los Angeles Times. “I am not in favor of using the higher forms like the chimpanzee. ”

Bailey was diagnosed with cancer in 2001 and chose to make his condition public, often seeming more curious than worried as it slowly advanced from his tongue to the rest of his body. He died May 12.

Baby Fae weighed all of 4.6 pounds when doctors determined she would likely die from hypoplastic left heart syndrome, a congenital heart defect that defied reconstructive surgery.

Because there were no infant human hearts immediately available, Bailey decided on a radical course — take the heart of a primate, in this case a baboon. Though the child died 21 days later, the surgery was seen as a pioneering step in medicine, and infant-to-infant heart transplants became an accepted procedure.

“When we operate on these babies, the hope is that they will live longer than us,” Bailey said in 2017 during a reunion with former transplant patients. “It’s nice to know that’s playing out.”

Baby Fae’s parents, who were never identified beyond their first names, backed his decision to use a heart from a primate to try to save, or at least extend, their daughter’s life.

“There are a lot of sentimental ways of talking about the heart, but it’s really just a pump,” the mother told People magazine. “The soul is not in the heart. The soul is in the brain.”

Bailey eventually performed 375 infant heart transplants, including the first infant-to-infant heart transplant.

Later in life, he pondered the legacy of the Baby Fae surgery. If he were able to perform it again, he said, he would have preferred to use a human heart. At the time though, he told the Times, none was available and time was running out.

Bailey also described what he called his “catastrophic” decision to use the heart of a baboon that had a different blood type. The child was type O, the baboon AB.

“If Baby Fae had the type AB blood group,” he told medical officials at a conference, “she would still be alive today.”