Q: How mitral valve orifice area can be guessed depending on clinical symptoms?

Answer: 

• The normal mitral valve orifice has a cross-sectional area of about 4.0 cm2.
• Usually patients are asymptomatic till orifice area is reduced to 2 cm2. 
• Mild symptoms may be present between 2 cm2 and 1.5 cm2.
• Most patients become symptomatic when mitral valve area is decreased to 1.5 cm2 (moderate/on exertion)
• If a patient symptoms are apparent, it can be easily guessed that mitral orifice area is at 1.0 cm2 or less. (even with mild exertion)

Combining with heart sounds auscultation, astute physician can predict valve area just on examination.