Using TTE, the stroke volume at the LVOT is obtained by measuring the diameter across the LVOT. The continuity equation assumes the aortic valve annulus is a perfect circle; because of this, any error in measuring the LVOT results in an under calculation of the aortic valve area. It is also important to consider that the anatomy of the aortic annulus is not circular, which also contributes to an inaccurate calculated AVA.