Human Heart Produces New Muscle Cells After Attack, Sydney Study Finds

A study published in Circulation Research has overturned one of cardiology's most durable assumptions: that the adult human heart cannot replace muscle cells lost to a heart attack.

Researchers at the University of Sydney, the Baird Institute, and Royal Prince Alfred Hospital collected tissue samples directly from patients undergoing bypass surgery, sampling both damaged and undamaged regions of the organ. <cite index="15-6">The study is also the first in the world to use tissue samples taken from living patients during bypass surgery.</cite> That methodological choice matters. Post-mortem or animal tissue introduces confounders that make translating findings to living human physiology genuinely difficult; working with fresh surgical samples gives the team a cleaner read on what the organ is actually doing at the moment of injury.

What they found was cardiomyocyte mitosis, ordinary cell division, occurring in heart muscle after infarction. <cite index="15-2">Though increased mitosis after a heart attack has been observed in the heart muscles of mice, this is the first time the phenomenon has been demonstrated in humans.</cite>

The clinical backdrop makes the finding worth paying attention to. <cite index="15-4">Heart attacks can eliminate a third of the cells in the human heart and, though survival rates have improved dramatically over the last decade thanks to therapeutic advancements, many patients still go on to develop heart failure, which can only be cured with a transplant.</cite> In Australia alone, <cite index="15-5">approximately 144,000 heart failure patients exist alongside only 115 heart transplants per year</cite>, a gap that makes any native regenerative capacity worth quantifying.

The crucial caveat, and the one that keeps this finding interesting rather than conclusive, is magnitude. <cite index="12-9">Researchers say this regeneration is not enough to fully restore heart function but could be enhanced in the future to improve recovery.</cite> The heart is not quietly fixing itself to pre-attack condition; it's producing a measurable but modest number of new cells alongside the scar tissue that remains the dominant response to injury.

First author Dr. Robert Hume, Lead of Translational Research at the Baird Institute, framed the significance carefully in remarks reviewed by Technology Networks: <cite index="11-11,11-12">"Until now we've thought that, because heart cells die after a heart attack, those areas of the heart were irreparably damaged, leaving the heart less able to pump blood to the body's organs. Our research shows that while the heart is left scarred after a heart attack, it produces new muscle cells, which opens up new possibilities."</cite>

Senior author Professor Sean Lal, a heart failure cardiologist at Royal Prince Alfred Hospital, pointed to a second output of the work: a living tissue model that the team plans to use to screen candidate therapies. <cite index="15-9,15-10">Using living human heart tissue models means the team will have more accurate and reliable data to develop new therapies for heart disease, and their samples have already identified several proteins previously shown to be involved in heart regeneration in mice.</cite>

That last point is where the real near-term scientific work sits. Demonstrating that cardiomyocyte division happens in humans is a necessary first step, but the pathway from "this occurs" to "we can amplify it safely" involves several layers the paper doesn't yet address: which molecular signals trigger the mitosis, whether newly divided cells integrate into functional myocardium or remain electrically isolated, and whether boosting the process risks arrhythmia. None of those questions diminish the finding, but they're the ones the field will need answered before anyone talks about a therapy.

The paper, authored by Hume, Warwick, Shim, and colleagues, is published in Circulation Research, volume 138, issue 2, under DOI 10.1161/CIRCRESAHA.125.327486.

Sources cited:
- Technology Networks (https://www.technologynetworks.com/cell-science/news/human-heart-regrows-muscle-cells-after-heart-attack-408774)
- University of Sydney News (https://www.sydney.edu.au/news-opinion/news/2026/01/20/human-heart-regrows-muscle-cells-after-heart-attack-world-first-study-shows.html)
- healthcare-in-europe.com (https://healthcare-in-europe.com/en/news/heart-regrow-muscle-cells-after-heart-attack.html)
- ScienceAlert (https://www.sciencealert.com/human-heart-tissue-actually-can-regenerate-after-a-heart-attack-new-study-shows)
- Circulation Research (AHA) (https://doi.org/10.1161/CIRCRESAHA.125.327486)