Severity of mitral stenosis is characterized echocardiographically as Moderate: Valve area > 1.5 to 2.5 cm 2 or diastolic pressure half-time < 150 msec Severe: Valve area ≤ 1.5 cm 2 or diastolic pressure half-time ≥ 150 msec; symptoms are often present However, the relationship between the area of the valve orifice and symptoms is not always consistent.