Virtually all cases of mitral valve stenosis are caused by rheumatic fever, which can follow an untreated strep throat infection. But many people who have mitral valve stenosis don't realize they had rheumatic fever.

In recent decades, cases of rheumatic fever have decreased considerably in Canada, the United States, and western Europe. But many people throughout the world still get rheumatic fever. This may include immigrants from regions where rheumatic fever is more common.

Other less common causes of mitral valve stenosis include:

• A congenital (from birth) heart defect that causes mitral valve stenosis in infants and young children.
• Infection of the mitral valve or the adjacent heart muscle (infective endocarditis).
• Metabolic disorders, such as Fabry's disease or Hurler-Scheie syndrome.
• Hardening of the mitral valve components (annulus and leaflets) due to aging.
• Hardening of the mitral valve due to severe kidney disease.
• Conditions that cause scarring of the mitral valve (lupus, rheumatoid arthritis, carcinoid syndrome).
• A noncancerous tumor in the left atrium (myxoma), which can also block blood flow across the mitral valve.
• The diet medicine fen-phen. Fen-phen was a popular diet drug that was taken off the U.S. market in 1997 because of its link to heart valve disease.