In the U.S. at any given time, thousands of adults and hundreds of children are on waiting lists for a lifesaving heart transplant, facing waits of six months or longer. Some will die in the interim, including one out of every eight children on the list. Worldwide, about 20 people die per day while waiting for any organ.

A promising advance from scientists in Germany offers a potential solution – a “heart patch” made from stem cells that could provide a bridge to transplantation, or maybe even a permanent fix. These patches of heart muscle – made from adult human stem cells – can be sutured onto a patient’s heart in a minimally invasive surgery to help it pump, the journal Nature reported. Each patch contains lab-grown cardiac tissue made of up to 200 million cells embedded in a collagen hydrogel. The patch, called engineered heart muscle, or EHM, was proven to work in rhesus macaques. The first human to get a patch was a 46-year-old woman in 2021, helping her survive until she could get a heart transplant.

The patches were then used on 15 other patients with severe heart failure, with more data on those cases expected by the end of the year. The innovation represents a step forward in the larger quest to solve the heart transplant crisis. About 50,000 people worldwide have end-stage heart failure, but only 5,000 heart transplants are performed annually because of the shortfall of donor hearts. At the same time, more than 6 million Americans live with heart failure, and that number is only expected to grow as the population ages. That makes the “bridge-to-transplant” development important, researchers say. Clinical trials may reveal whether this could one day end the need for a transplant altogether.

What’s remarkable about the heart muscle patches is they can be engineered from induced pluripotent stem cells (iPSCs), as opposed to embryonic stem cells, which present ethical issues. iPSCs are reprogrammed from adult stem cells to become any cell type in the body – in this case, cardiomyocytes in the heart. Arrhythmia or tumor growth can occur when pluripotent stem cells are put into tissue, as the organ may reject the new cells, or the heart may develop issues with its own electrical system. But that didn’t happen with the new heart patch.

As to whether these patches can be brought up to scale, pharmacologist Sian Harding, PhD, was certain they could. “I’ve made these patches myself,” said Harding, an emeritus professor of cardiac pharmacology at Imperial College London, and author of The Exquisite Machine: The New Science of the Heart. She estimated a cost of about $15,000 “to make a really solid piece of tissue about the size of your palm that would cover up the heart damage from a heart attack.” That’s not unreasonable for a heart implant, she said.