Acute rheumatic fever is an autoimmune process that can follow pharyngeal infection with Group A beta hemolytic Streptococcus (S. pyogenes). Microscopically, acute rheumatic carditis is marked by a peculiar form of granulomatous inflammation with so-called "Aschoff nodules" seen best in myocardium. The myocarditis may be severe enough to cause congestive heart failure. Here is an Aschoff nodule. The most characteristic component is the Aschoff giant cell. Several appear here as large cells with two or more nuclei that have prominent nucleoli. Scattered inflammatory cells accompany them and can be mononuclears or occasionally neutrophils.