In these clinical settings, knowledge of the severity of valve obstruction and LV function is critical for optimiz- ing loading conditions and maintaining a normal car- diac output. 3.2.1.3. Diagnostic Testing: Routine Follow-Up Timing of periodic clinical evaluation of asymptomatic patients with severe AS depends on comorbidities and patient-specific factors, as well as AS severity (Table 4). When severe AS is present (aortic velocity 4.0 m/s), the rate of progression to symptoms is high, with an event-free survival rate of only 30% to 50% at 2 years. In patients with asymptomatic severe AS, peri- odic monitoring is needed because symptom onset is insidious and may not be recognized by the patient. With moderate AS (aortic velocity 3.0 3.9 m/s), the average annual rate of progression is an increase in ve- locity of 0.3 m/s, increase in mean pressure gradient of 7 mmHg, and decrease in valve area of 0.1 cm2 . There is marked individual variability, with more rapid progression in older patients and in patients with more severe leaflet calcification. In patients with aortic scle- rosis, defined as focal areas of valve calcification and leaflet thickening with an aortic velocity <2.0 m/s, pro- gression to severe AS occurs in about 10% of patients within 5 years. Patients with BAV disease are also at risk of progressive valve stenosis, with AS being the most common reason for intervention in patients with a BAV (Section 5.1.1).1 13 3.2.1.4. Diagnostic Testing: Cardiac Catheterization Diagnostic TTE and Doppler data can be obtained in nearly all patients, but severity of AS may be underes- timated if image quality is poor or if a parallel intercept angle is not obtained between the ultrasound beam and aortic jet. 