The heart produces new muscle cells, which opens up new possibilities.
For generations, medicine held that a damaged heart was a permanently diminished one — that the muscle lost to a heart attack could never return. Researchers in Sydney have now quietly dismantled that assumption, confirming for the first time in living human patients what had only been glimpsed in mice: the human heart does, in fact, regenerate its own muscle cells after injury. The discovery, drawn from tissue collected during bypass surgeries at Royal Prince Alfred Hospital, does not promise a cure, but it opens a door that many believed was sealed — the possibility that the heart, given the right guidance, might one day be taught to heal itself more fully.
- A foundational belief in cardiology — that heart muscle lost to a heart attack is gone forever — has been overturned by direct evidence from living human tissue.
- The gap between need and remedy is stark: 144,000 Australians live with heart failure, yet fewer than 115 transplants are performed each year, leaving most patients without a path to recovery.
- Scientists identified new muscle cells actively dividing in damaged hearts during bypass surgery, the same regenerative process seen in rodents but never before confirmed in people.
- The team has developed a first-of-its-kind method for studying living cardiac tissue pre-mortem, creating a reliable platform to test therapies and identify the proteins driving natural regeneration.
- Researchers are now working to amplify the heart's own repair signals — aiming not just to understand regeneration, but to turn it into a clinical tool capable of reversing heart failure itself.
For decades, cardiologists held a grim certainty: heart attack damage is permanent. Scarred tissue stays scarred. Lost pumping power does not return. Researchers at the University of Sydney have now overturned that assumption, publishing evidence in Circulation Research that human hearts do regenerate muscle cells after a heart attack — a process previously confirmed only in mice.
The discovery came through an unusual window. During bypass surgeries at Royal Prince Alfred Hospital, surgeons collected tissue from both healthy and damaged regions of patients' hearts. Analyzing these living samples, the team found something striking: even as scar tissue formed, the heart was producing new muscle cells through mitosis. The regeneration was real — but insufficient on its own to restore full function or prevent the scarring that follows a heart attack.
Lead author Dr. Robert Hume described the finding as a capacity that had been hidden in plain sight. The heart's natural repair process, long dismissed as nonexistent, is simply too modest to undo the damage alone. But if researchers can identify the proteins and signals driving it, they may be able to amplify that process — coaxing the heart toward more complete healing.
The stakes are considerable. Cardiovascular disease accounts for roughly a quarter of all deaths in Australia. A single heart attack can destroy up to a third of the heart's muscle cells, and many survivors go on to develop chronic heart failure. With only about 115 transplants performed annually against a population of 144,000 Australians living with the condition, the treatment gap is vast.
Senior author Professor Sean Lal, a heart failure cardiologist, sees the long-term goal as harnessing regeneration to reverse heart failure itself. Crucially, the team has also established a first-of-its-kind method for collecting and studying living cardiac tissue from surgical patients — a more accurate testing ground than animal models alone. Several proteins involved in mouse heart regeneration appear to function similarly in humans, suggesting that the translation from rodent biology to human medicine may be closer than once imagined. For those living with the aftermath of a heart attack, that possibility carries a weight that medicine has rarely offered them before.
For decades, cardiologists have operated under a grim certainty: when a heart attack destroys muscle tissue, that damage is permanent. The scarred area remains scarred. The lost pumping power never returns. Now, researchers in Sydney have overturned that assumption. In work published in Circulation Research, they have demonstrated for the first time that human hearts do, in fact, regenerate muscle cells after a heart attack—a process scientists knew happened in mice but had never confirmed in living people.
The discovery emerged from an unusual opportunity. During bypass surgery at Royal Prince Alfred Hospital, surgeons collected tissue samples from both healthy and damaged regions of patients' hearts. Using techniques developed by Professors Paul Bannon and Sean Lal, the research team analyzed these living samples in the laboratory, looking for signs of cellular activity in the weeks and months following a heart attack. What they found was striking: the heart was producing new muscle cells, even as scar tissue formed. The cells were dividing and multiplying in a process called mitosis—the same regenerative response researchers had observed in rodent hearts but never before confirmed in humans.
Dr. Robert Hume, the study's lead author from the University of Sydney and the Baird Institute, framed the finding with careful optimism. The heart's natural ability to generate new cells, he explained, had been hidden in plain sight. Doctors had assumed that because cells died during a heart attack, the damage was irreversible. The new evidence suggests otherwise. Yet Hume was quick to add a crucial caveat: the regeneration happening in the heart is not enough, on its own, to prevent the devastating consequences of a heart attack. The scar tissue remains. The heart's pumping capacity is still compromised. But the discovery opens a door. If researchers can identify which proteins and signals drive this natural regeneration, they might be able to amplify the process—to coax the heart into healing itself more completely.
The stakes are substantial. Cardiovascular disease kills more people worldwide than any other condition, accounting for nearly a quarter of all deaths in Australia alone. A single heart attack can destroy up to one-third of the heart's muscle cells. While survival rates have improved dramatically over the past decade thanks to better emergency care and medications, many survivors develop heart failure—a chronic condition in which the heart can no longer pump blood efficiently to the body's organs. In Australia, roughly 144,000 people live with heart failure. Yet only about 115 heart transplants are performed each year in the country, leaving a vast gap between those who need new hearts and the supply available.
Professor Sean Lal, the study's senior author and a heart failure cardiologist, articulated the long-term vision. The goal is not merely to understand regeneration but to harness it—to develop therapies that could reverse heart failure itself. By working with living human heart tissue rather than relying solely on animal models or computer simulations, the team has created a more accurate testing ground for new treatments. Already, their analysis has identified several proteins involved in heart regeneration in mice that appear to play similar roles in human hearts. That translation from rodent biology to human medicine is where the real promise lies.
What makes this work particularly significant is the method itself. The researchers developed a reliable way to collect and study living heart tissue from conscious patients undergoing surgery. This approach—gathering samples before death, hence the term "pre-mortem"—had never been systematized for cardiac research before. It creates a laboratory model that can be used to test new therapies and identify which interventions might work in real human hearts. The door is now open not just to understanding how hearts regenerate, but to learning how to make that regeneration work harder, faster, and more completely. For the millions of people living with the aftermath of a heart attack, that possibility represents something that medicine has long denied them: hope for genuine repair.
Citas Notables
While the heart is left scarred after a heart attack, it produces new muscle cells, which opens up new possibilities.— Dr. Robert Hume, lead author
The goal is to use this discovery to make new heart cells that can reverse heart failure.— Professor Sean Lal, senior author
La Conversación del Hearth Otra perspectiva de la historia
So the heart was already trying to heal itself all along, and we just didn't know it?
Exactly. We've been looking at scarred tissue after a heart attack and assuming that was the end of the story. But the cells were actually dividing, creating new muscle tissue. We missed it because we weren't looking at living tissue from actual patients.
Why does it matter that they used tissue from living people instead of just studying mice?
Mouse hearts and human hearts are different in important ways. What we see in a mouse might not translate directly to humans. By analyzing actual human tissue, they can identify which proteins and signals are really at work in our hearts, not just in rodents.
But you said the regeneration isn't enough to prevent the damage. So what's the point?
The point is that the heart has a natural capacity we can potentially amplify. Right now, the regeneration is happening but it's incomplete—the scar tissue still forms, the pumping power is still lost. If we can understand what's driving that regeneration and boost it, we might be able to prevent heart failure altogether.
How close are we to actual treatments?
This is foundational work. They've confirmed the process exists in humans and created a way to study it reliably. The next step is identifying which therapies can enhance it. That could take years, but they now have a clear target and a method to test approaches.
What about the people with heart failure right now?
That's the urgency. There are 144,000 Australians living with heart failure and only 115 transplants available each year. This research is aimed at eventually giving those people an alternative to waiting for a donor heart—the possibility of their own heart healing itself.