METHODS, STATISTICAL ANALYSIS & DATA MANAGEMENT Patients will be classified as severe or non-severe AS based on aortic valve area calculation as per ACC/AHA guidelines. Thus, patients with AVA ≤ 1.0 cm2 will be considered severe AS. This will also be evaluated using two other widely used criteria for aortic valve area indexed for body surface area. Severe AS will be considered as AVAi ≤ 0.6 cm2 (guidelines) or ≤ 0.5 cm2 (Braunwald's text, Grayburn). Using these three definitions, any patient who also has a peak velocity ≥ 4.0 m/s or a mean gradient ≥ 40 mmHg will be considered to definitely have severe AS. Patients with values < 4.0 m/s or < 50 mmHg will be further classified by stroke volume index < 35 mL/m2 to have low flow, low gradient severe AS. Further classification will be based on LVEF ≥ 50% or <50%. The former will be considered to have paradoxical low flow, low gradient severe AS with preserved LVEF (Hachicha, Circ 2007) or traditional low flow, low gradient severe AS (Tandon, Grayburn JACC Imaging 20130> The above criteria will be used to reclassify patients when LVOT cross-sectional area is determined by CT scan instead of echocardiography. Reclassification will occur with CT measurements of LVOT for AVA and SVI, both of which are dependent on LVOT area, generalized linear mixed model (GLMM) with a logistic link function will be used to assess whether differences in classification exist.