左心房可见二尖瓣，呈特有的鱼口状狭窄，并有慢性风湿病瘢痕。风湿性心脏病时二尖瓣最易受累，其次为二尖瓣和主动脉同时受累，然后是主动脉单独受累，二尖瓣、主动脉和三尖瓣同时受累最不常见。
The heart has been sectioned 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. Mitral valve is most often affected with rheumatic heart disease, followed by mitral and aortic together, then aortic alone, then mitral, aortic, and tricuspid together.