- Fibrous endocarditis is a late stage in development of rheumatic endocarditis. It is the usual finding of acquired valve defect.
- The mitral valve is mostly affected with both stenosis and/or insufficiency.
- Valve cusps are thickened and vascular. At some places the tissue shows basophilia (bluish), sign for redistribution and focal accumulation of glycosaminoglycans from earlier stages of endocarditis. These sections show metachromasia with toluidine blue (shift of the blue stain to purple because of the chemical content of the tissue).
- Similar changes are seen in chords, capturing the valvar cusps.