i
AVA = ( LVOT CSA x LVOT Vmax ) : AV Vmax

LVOT Vmax: PW, Apical 5C view or Apical 3C view.
AV Vmax: CW, Apical 5C view or Apical 3C view or Suprasternal view or Right Parasternal view.

LVOT Vmax - maximum Left Ventricular Outflow Tract Velocity
AV Vmax - maximum Aortic Valve Velocity