Doctors in Japan were treating a 60-year-old man's irregular heart rhythm when an ultrasound picked up something unexpected: a small, partly calcified lump on the wall of his heart's right upper chamber. Blood thinners did not make it go away, and no one could rule out a tumor.
Surgeons removed the mass through a small incision in the side of his chest. Under the microscope, it turned out to be neither cancer nor a true tumor, but a long-standing blood clot that had hardened, scarred, and partly calcified.
