For decades, myocardial infarction has been treated as a one-way biological event: heart muscle cells die, scar tissue forms, and functional loss is permanent. A new study challenges that framework, not by claiming the heart can fully repair itself, but by showing that regeneration does, in fact, occur in humans.
Researchers at the University of Sydney report the first definitive demonstration of cardiomyocyte regrowth in adult human hearts following myocardial infarction. Published in Circulation Research, the study provides direct evidence that heart muscle cells can re-enter the cell cycle and complete division — an observation previously confined to animal models.
Crucially, the finding is not based on indirect markers or inferential data. “We were able to show a statistically significant increase in cardiomyocyte mitosis in infarcted human hearts,” first author Robert Hume told DDN. “Importantly, we showed cardiomyocytes at all stages of mitosis, including the last stage known as cytokinesis.”
Why this evidence has been missing — until now
The central barrier to demonstrating human cardiac regeneration has not been conceptual, but technical. Most prior studies relied on post-mortem heart tissue collected hours after death — long after the molecular signals associated with cell division begin to degrade.
This study sidestepped that limitation by using pre-mortem human heart tissue collected either during coronary bypass surgery or shortly after life support withdrawal, allowing the tissue to be preserved in its native biological state.
“The use of pre-mortem tissue meant that the heart tissue could be preserved in its native state,” Hume said. “We were able to snap freeze the tissue in liquid nitrogen within 15 minutes… allowing us to capture cardiomyocytes in mitosis.”
That timing proved critical. Proteins expressed during mitosis are short-lived, and delayed sampling can obscure or erase evidence of cell division altogether. By preserving tissue rapidly, the researchers were able to detect mitotic activity that would likely have gone unnoticed using conventional approaches.
The result is a clearer answer to a long-standing question in cardiovascular biology: the adult human heart is not completely incapable of regeneration — it is simply very limited.
Regeneration without recovery
The study does not suggest that cardiomyocyte regrowth is sufficient to restore heart function after a major infarction. On the contrary, the researchers emphasize that the scale of regeneration observed is biologically meaningful but functionally inadequate.
“The damage and cardiomyocyte cell death that occurs far outweighs the new cardiomyocytes being formed,” Hume noted. “People who experience a significant infarct have hearts that pump less effectively.”
That distinction is critical for clinicians and drug developers alike. The finding reframes heart failure not as a condition devoid of regenerative capacity, but as one in which endogenous repair mechanisms exist — and fail to keep pace with injury.
That gap, the authors argue, may represent a therapeutic opportunity. Rather than introducing external cells or relying solely on mechanical support, future interventions could aim to amplify the heart’s intrinsic regenerative response.
The team also identified genes and proteins in human samples that have previously been implicated in cardiac regeneration in mice, lending cautious support to select animal models while reinforcing the need for human-specific validation.
“Our early findings increase the possibility that these proteins are important in human cardiac regeneration,” Hume said, while cautioning against assuming causality. “Whether something is upregulated versus has a specific effect on cardiac regeneration is yet to be tested.”
Access to living human heart tissue, the researchers argue, could now enable that next phase — allowing potential therapies to be evaluated in biologically relevant human models before entering the clinic.
For now, the study redraws an important boundary: heart regeneration in humans is real, measurable, and limited. Whether it can be meaningfully enhanced remains an open — and consequential — question.
