Etiology: metaplasia caused by group A beta-hemolytic streptococcal infection Basic lesion Metaplasia Exudative phase in the connective tissue stroma of the heart, plasma membranes, joints, and skin exhibits fibrinoid necrosis of mucin-like degenerative nuclear collagen fibers. A small amount of lymphoid c, plasma c, and mononuclear c infiltrate. In the proliferative phase (granulomatous phase), myocardial interstitium, endocardium, and subcutaneous connective tissue are edematous, proteoglycans are increased, and Aschoff cells (interstitial myocardial ones are mostly located in the paravalvular, large, cytoplasm-rich, basophilic, and resemble lord’s eye or caterpillar in nuclear section) are present, and they are subaggregated into Aschoff vesicles, which are characteristic lesions and have diagnostic significance. In the scar phase (healing phase), necrotic cells in Aschoff vesicles are gradually absorbed, Aschoff cells become fibroblasts, rheumatic vesicles are fibrotic, and finally form a pyknotic scar. (A) Rheumatic heart disease Rheumatic endocarditis lesions mainly involve the heart valves, the mitral valve is the most common, followed by the mitral valve and aortic valve at the same time. The valves are swollen, with mucus-like degeneration, fibrinoid necrosis, plasma exudate, and inflammatory cell infiltration. A single row of white translucent redundant organisms, composed of platelets and fibrin, appear on the atretic edge of the valve, which are firmly attached and do not easily fall off. As a result of repeated attacks, the valve is deformed and adherent, the tendon cords are thickened and shortened, and the valve orifice is narrowed or incompletely closed. Rheumatic myocarditis mainly involves the interstitial connective tissue of the heart muscle. Rheumatic granulomas are formed. Rheumatic epicarditis mainly involves the dirty layer of epicardium and is plasmacytotic or fibrinitis. Formation of choroidal heart. (b) Rheumatoid arthritis Large joints, wandering, recurrent, inflammatory reaction. There are usually no sequelae. (iii) Skin lesions Circumscribed erythema (exudative inflammation); subcutaneous nodules (proliferative inflammation) (iv) Rheumatic arteritis Involvement of the middle arteries (coronary, renal, mesenteric, cerebral arteries). (v) Rheumatic encephalopathy Involvement of the extrapyramidal system may result in small chorea.