Cattle have a bone in the heart. So do camels and otters. Humans, the anatomy textbooks say, do not.
Then medical examiners in Virginia sliced the conduction system out of a 39-year-old man's heart, cut it into thin sections, and found one.
The structure was boomerang-shaped, roughly the size of a black bean at 0.8 by 0.6 by 0.4 centimeters, and it sat inside the triangle of Koch in the right atrium, at the location of the atrioventricular node. That node is the relay station carrying every electrical signal from the upper chambers of the heart to the lower ones. Under the microscope, the structure was mature bone containing trilineage hematopoietic elements, meaning it held functioning marrow producing all three major blood cell lines.
Mehrnoosh Ghandili and Mark A. Giffen Jr. of the Virginia Office of the Chief Medical Examiner published the finding in the American Journal of Forensic Medicine and Pathology, titling it the first report of ossa cordis in a human heart. It appeared online in February 2025 and in print that September, and drew fresh attention in February 2026 when Live Science covered the case.
The Man Was Not Being Examined for His Heart
He had died after a fight, from a stab wound to the chest that punctured a vein in his lungs. The heart examination was routine, and the bone was incidental.
His heart was enlarged and showed moderate atherosclerosis in the left anterior descending and right coronary arteries. Beyond that, it was normal, with no fibrosis, no valve abnormalities, and no degenerative changes. That detail matters, and it is the part that complicates the tidy explanations.
In animals that reliably carry an os cordis, such as cattle, the bone is considered normal anatomy and is thought to help maintain the heart's shape during contraction and support the valves. In species where it appears sporadically, such as dogs, it has been associated with disease.
What the Chimpanzee Study Suggested, and Where This Case Diverges
The strongest recent comparison comes from great apes. In 2020, a team at the University of Nottingham scanned 16 chimpanzee hearts using X-ray microtomography and published the results in Scientific Reports. A dense structure appeared in four hearts. On closer examination, two contained trabecular bone, one contained hyaline cartilage, and one showed mineralized fibrocartilaginous change with bone formation underway.
The pattern was consistent. Every heart with marked myocardial fibrosis showed bone or cartilage formation, and hearts without it showed none. That association led the authors to suggest an os cordis in chimpanzees may be a marker of disease rather than normal anatomy. Catrin Rutland, who directed the research, said at the time that the discovery raised the question of "whether some people could have an os cordis too."
That question now has one answer, and it does not fit the chimpanzee pattern neatly. The Virginia case had no fibrosis at all. The authors note that the formation might still relate to his enlarged heart and coronary disease, and that age and disease influence the structure in other species, but they were working without his full medical history.
A Long-Running Argument About What Is Actually In There
Human hearts are not a blank slate on this question. Also in 2020, Argentine cardiac surgeon Jorge Trainini and colleagues described a structure they called the cardiac fulcrum, proposing that it anchors the heart muscle as it pumps. Dissecting bovine and human hearts, they reported a bony matrix in cattle but a tendinous one in adult humans, with chondroid tissue in a 10-year-old's heart and in fetal specimens.
Trainini told Live Science the os cordis and the cardiac fulcrum are the same thing. The Virginia authors disagree. They acknowledge his work but argue their finding is distinct because it was true bone.
Both camps converge on one conclusion. Trainini has said his subsequent examinations of roughly 100 human hearts lead him to think all humans have a cardiac fulcrum. The case report authors likewise suggest the structure may be more common in people than currently recognized.
The reason nobody has noticed comes down to method. The bone was found only because the examiners sectioned the conduction system in detail, which is not standard practice at autopsy. Anything sitting in the triangle of Koch would simply never be looked at.
What This Does and Does Not Mean for Living Patients
Nothing about this changes clinical care today. This is a single incidental finding in one deceased person, discovered during a death investigation for an unrelated cause. It establishes that mature bone can form at the human atrioventricular node. It does not establish how often that happens, whether it affects heart rhythm, or whether it can be detected in a living person.
The location is the reason cardiologists may find it interesting. The atrioventricular node governs the timing between the upper and lower chambers, and structural change in that region has been described in other contexts, including nodal tumors, as a route to conduction abnormalities and sudden death. Whether an os cordis does anything electrically in humans is unknown, and this report does not test it.
The authors frame the finding as a question rather than a discovery with consequences: whether an os cordis in humans and primates reflects degenerative heart disease, or is simply part of normal mammalian heart development and aging that has gone unrecorded because nobody sliced thin enough. The authors reported no conflict of interest.
Key Questions Answered
What is an os cordis?
It is a bone that forms within the fibrous skeleton of the heart. It is normal anatomy in some large mammals, including cattle and camels, where it is thought to support heart shape and valve function.
What exactly did the examiners find?
A boomerang-shaped bone measuring 0.8 by 0.6 by 0.4 centimeters at the location of the atrioventricular node in the right atrium of a 39-year-old man. Microscopy showed mature bone with active marrow.
Was this what killed him?
No. He died from a stab wound to the chest. The bone was an incidental finding during autopsy.
Do all humans have one?
Unknown. The case report authors and a separate Argentine research group both suspect the structure may be more common than recognized, but that has not been established.
Why has this not been found before?
The bone was located only because examiners sectioned the heart's conduction system in detail, a step not routinely performed at autopsy.
Could this cause heart rhythm problems?
There is no evidence either way. The location sits at the heart's electrical relay, which is why the finding drew attention, but this single case did not test any effect on rhythm.
