The pathognomonic feature of rheumatic hea disease is

During acute RF, distinctive lesions occur in the hea, called Aschoff bodies, consisting of foci of T lymphocytes, occasional plasma cells, and plump activated macrophages called Anitschkow cells (pathognomonic for RF). These macrophages have abundant cytoplasm and central round-to-ovoid nuclei (occasionally binucleate) in which the chromatin condenses into a central, slender, wavy ribbon (hence the designation "caterpillar cells").