The heart has been opened at autopsy to reveal the mitral valve as seen from above in the left atrium. The mitral valve demonstrates the typical "fish mouth" shape with chronic rheumatic scarring. The mitral valve is most often affected with rheumatic heart disease, followed by mitral and aortic valves together, then aortic valve alone, then mitral, aortic, and tricuspid valves together. Rheumatic heart disease is an immunologically mediated disease following group A beta hemolytic streptococcal infections.

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