American David Bennett, 57, died in March of this year of heart failure, not a rejection of the transplanted pig heart he received. That’s why doctors involved in the first transplant of its kind still consider it a success.

In January, the US patient became the first person in the world to receive a genetically modified heart transplant from a pig. It has been judged unsuitable for human transplant – a decision usually made when a patient’s health is in very poor condition.

According to NBC News, doctors participating in the University of Maryland Medical study said in an article last month that “a complex set of factors” cause heart failure, according to a press release.

Co-leader of the study, Dr. Bartley Griffith, a professor of transplantation at the University of Maryland School of Medicine and also clinical director of the college’s heart xenotransplantation program.

“Instead, we saw the heart muscle thickening and then stiffening, leading to diastolic heart failure, which means the heart muscle was unable to relax and fill the heart with blood as it should,” he added.

Possible causes

Participants in the studies said the heart may have failed because a drug that was supposed to prevent rejection and infection could damage the muscles.

“The heart also contained DNA evidence of a latent swine virus called porcine cytomegalovirus, which was detected by highly sensitive testing a few weeks after surgery and later confirmed during autopsy of the organ,” the statement said.

The possibility of the virus damaging the heart is being investigated.

Also, according to NBC News, those involved in the transplant reported that infection control measures were in place and that the heart was tested shortly before the procedure. Infection was confirmed at autopsy.

Co-leader of the study, Dr. Muhammed M. Muhiddin. “Knowing what we know now, we will change some of our practices and techniques in the future.”