Mitral valve stenosis is a heart condition in which the mitral valve—which regulates blood flow on the left side of the heart—fails to open as wide as it should. Although it has no immediate effect on health, eventually mitral valve stenosis can cause the left atrium to work harder to pump blood through the narrowed valve, leading to heart failure and complications such as stroke, heart rhythm problems (such as atrial fibrillation), fluid buildup in the lungs, and blood clots.

Symptoms usually do not develop for 10 to 20 years, and may take as long as 40 years. Early symptoms, such as shortness of breath with exertion, are often mild and hard to distinguish from other forms of heart disease. In the later stages of mitral valve stenosis, blood may back up into the lungs, causing symptoms such as shortness of breath, fatigue, weakness, and pounding of the heart.

Treatment for mitral valve stenosis depends on whether symptoms are present and the amount of narrowing in the mitral valve. Close monitoring is usually all that's needed for those who have mild or no symptoms, but a doctor may recommend surgery to repair or replace the valve if symptoms and severe narrowing are present.