Are Heart Muscle Cells as Old as We Are?

A Time Marker from the Atmosphere

During the Cold War, above-ground nuclear weapons tests sharply increased the carbon-14 content of the atmosphere. This carbon entered the body through plants and food. When a cell forms new DNA, it incorporates this carbon. Comparing the DNA's carbon-14 content with the atmospheric curve of the time allows an estimate of the age of the DNA population studied, not an exact dating of each individual cell.[1]

In 2009, Bergmann and colleagues used this time marker for human heart muscle cells. The method dates DNA. It does not observe cell division and does not show where new cells come from.[1]

Why Cell Type and Cell Nucleus Matter

In the 2015 study, heart muscle cells made up just under one fifth of all cells in the left ventricle of young adults. Other cell types renew themselves much faster: in the same study, the cells of the inner vessel wall were on average only about six years old.[2] A sample from the heart muscle as a whole therefore says little about the heart muscle cells.

The research team therefore sorted cell nuclei by cell type and measured their DNA. What was measured, then, was nuclei, not whole cells. In this study, about one in four heart muscle cells had more than one nucleus, which the analysis had to take into account.[2]

More DNA Does Not Automatically Mean More Cells

Heart muscle cells can form additional copies of their DNA without dividing. The 2015 study observed this in the left ventricle mainly in the second decade of life.[2] This DNA also carries the atmospheric time marker and must not be mistaken for new cells.[1]

The 2015 study therefore combined the measurements with cell counts, the DNA content of the nuclei and mathematical models. According to this analysis, the number of heart muscle cells remains constant from around the time of birth onward, and renewal is highest in early childhood. For the left ventricle, the model yielded 0.8 percent per year at age 20 and 0.3 percent at age 75.[2]

According to the 2015 analysis, the heart muscle cells of the adults studied were on average about five years younger than the person themselves.[2]

These are estimates based on model assumptions, not new cells counted in each heart. For the carbon-14 dating of heart muscle cell DNA, 51 deceased people aged between 8 and 75 years were studied; this number does not describe all the sub-studies of the paper. Hearts with signs of disease were excluded. In 2015, the authors described a dispute in the literature at that time: other studies had reported anything from no replacement to complete replacement every few years.[2]

Renewal Is Not Yet Recovery

A renewal rate does not imply that a damaged heart regains its function. The 2015 study examined cell turnover in hearts without signs of disease, not a treatment after a heart attack. That the authors see in it a starting point for future therapies is an outlook, not proof of efficacy.[2]

A 2025 study found low renewal rates in advanced heart failure, but higher rates in a subgroup with functional recovery on a heart support pump.[3] This group comparison does not establish a causal effect of the pump.

The measurement answers a narrow question: what age can be estimated for the DNA population in the nuclei of a particular group of cells? Everything beyond that, from cell numbers to clinical significance, requires additional assumptions or other studies.

Note: This article places three published studies in context. No measurements of our own were carried out.