Infection with the as yet unidentified rheumatic virus was for a long time associated only with a special type of febrile nonsuppurative polyarthritis, fleeting from joint to joint, usually leaving the joint attacked free from permanent injury, and reacting to salicylates with decrease of pain and temperature. Later, it was recognized that the same virus was capable of producing lesions in the valvular and mural endocardium, myocardium, pericardium, central nervous system (chorea), subcutaneous tissue (fibroid nodules), and adventitia and media of the thoracic aorta. Though the Aschoff body, the typical microscopic lesion of rheumatic fever, is most often found in the myocardium, perivascular lesions closely resembling it have been demonstrated in some of the conditions mentioned above, which are now recognized as definitely of rheumatic origin. The presence of the Aschoff body, therefore, serves as histopathologic evidence of rheumatic virus infection in the etiologic diagnosis of obscure clinical conditions. It