For decades, the working assumption in cardiology has been simple and grim: once heart muscle dies during a heart attack, it’s gone for good. A new study from the University of Sydney, the Baird Institute, and Royal Prince Alfred Hospital challenges that assumption directly, with evidence, for the first time, that human heart muscle cells can regrow after a heart attack.

Not as Irreparable as Once Thought

A heart attack can destroy as much as a third of the cells in the human heart. Scientists had already observed increased mitosis, the process by which cells divide and multiply, in the hearts of mice after a heart attack, but nobody had shown the same thing happening in humans. This study is the first to do it.

“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,” said first author Dr. Robert Hume, from the Faculty of Medicine and Health and Charles Perkins Centre at the University of Sydney, and Lead of Translational Research at the Baird Institute. “Our research shows that while the heart is left scarred after a heart attack, it produces new muscle cells, which opens up new possibilities.”

That said, the researchers are careful to temper expectations. The heart’s natural regenerative response isn’t currently strong enough to replace all of the muscle lost during an attack. As Hume put it, the discovery “isn’t enough to prevent the devastating effects of a heart attack” on its own, the hope is to eventually find ways to amplify this natural repair process.

A New Research Tool: Living Heart Tissue

Part of what makes this study notable is how the researchers got their data. Rather than relying solely on animal models or post-mortem tissue, the team collected “pre-mortem” heart tissue samples from consenting patients undergoing bypass surgery at Royal Prince Alfred Hospital, sampling both diseased and non-diseased areas of the heart. The technique was developed by Professor Paul Bannon and Professor Sean Lal, who work jointly across the University of Sydney, RPA Hospital, and the Baird Institute.

Because the tissue comes from living human hearts rather than animal models or cadavers, it gives researchers a laboratory model that may track much more closely with what’s actually happening inside patients, a potentially significant tool for future cardiac research.

Why This Matters: The Heart Failure Gap

Cardiovascular disease remains the world’s leading cause of death, accounting for roughly a quarter of all deaths in Australia. Many people who survive a heart attack go on to develop heart failure, where the heart can no longer pump blood effectively. Right now, a heart transplant is the only cure, but transplants are scarce. Australia has an estimated 144,000 people living with heart failure, yet only around 115 heart transplants are performed there each year. That gap is exactly what makes a regenerative approach so appealing: a therapy that helps the heart repair itself wouldn’t depend on a matching donor organ.

What Comes Next

Professor Sean Lal, the study’s senior author and a heart failure cardiologist at RPA Hospital, framed the long-term goal plainly: “Ultimately, the goal is to use this discovery to make new heart cells that can reverse heart failure.” Using the living tissue model, the team says it has already identified several proteins previously linked to heart regeneration in mice, raising the exciting possibility that some of the same biological pathways could be at work in humans, and could eventually be targeted with new therapies.

The study was published in Circulation Research.

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