Hospitals around the country are facing major organ shortages. In 2024, the U.S. performed 4,636 heart transplants. Despite many procedures, hundreds of patients are left waiting each year for a new organ.

A glaring factor for heart transplants is that doctors prefer hearts from donors younger than 45. However, a new study from Harvard University suggests that older hearts could be used safely.

Hearts Changing Their Biological Age

Photo: Canva

Researcher Jesse Poganik and his team wanted to understand what happens to a heart after a transplant. They started their study on mice, grafting young hearts into old mice and old hearts into young mice. After a few months, they checked the tissue for cellular damage to measure biological age.

The donated hearts actually changed their biological age to match their new host. An old heart in a young mouse seemed to get younger, while a young heart in an old mouse aged faster.

Next, the team looked at human medical records from Brigham and Women’s Hospital. They found 11 cases in which the donor and recipient had a large age gap.

“The remarkable thing is that we found the same effects that we saw in the mice,” said Poganik.

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The human hearts took on the biological age of their new owners. When researchers checked medical records a year after surgery, data like heart rate and exercise capacity usually matched the recipient’s age, not the donor’s.

“Some, but not all, functional measures tracked the prediction that these older hearts in younger individuals functioned as if they were biologically younger, and vice versa,” Poganik explained. “Some things are probably simply irreversible.”

Expanding Heart Transplants

Surgeons currently hesitate to give old hearts to young patients because they worry that the organ won’t last very long. However, this study implies that older hearts will “age backward” in a younger body.

“This brilliant study is aligned with new science to understand aging and the effect of blood factors that might hold the answers to the ‘fountain of youth’,” said Bartley Griffith, a surgeon who performed the first genetically modified pig heart transplant in 2022.

The biggest takeaway here is that if hospitals could start using older donor hearts, then it could potentially shorten transplant waiting lists.

“Will there now be a rush to use older donor hearts not just in older recipients but perhaps by targeting young patients who might mitigate the advanced cellular senescence of an older organ?” Griffith added. “This work has the potential to increase the use of older donor hearts and likely all organs for the young waiting on transplant lists.”

“What a ride we are on!” Griffith emphasized.