Aortic Valve Area Calculator (continuity equation, AS severity)

Understanding the aortic valve area calculator — concept and principle

This calculator estimates the aortic valve area (AVA) with the continuity equation from echocardiographic measurements: LVOT diameter, LVOT velocity-time integral and aortic valve velocity-time integral. It also gives the indexed AVA, the LVOT area, the VTI ratio and the aortic stenosis severity grade for each measure. Cardiology trainees, sonographers and students use it.

Same flow through a narrow valve — with the default inputs: 0.79 cm².

How it is calculated

LVOT area CSA = π × (D ÷ 2)²
AVA = CSA × VTI(LVOT) ÷ VTI(AV)
Indexed AVA = AVA ÷ body surface area
VTI ratio (dimensionless index) = VTI(LVOT) ÷ VTI(AV)
ASE/EACVI 2017 grades: AVA over 1.5 mild, 1.0–1.5 moderate, under 1.0 cm² severe; indexed over 0.85, 0.60–0.85, under 0.6 cm²/m²; VTI ratio over 0.50, 0.25–0.50, under 0.25

The principle

The continuity equation rests on conservation of flow: the blood leaving the ventricle through its outflow tract in each beat must also pass through the aortic valve. Stroke volume equals area × velocity-time integral at both places, so the valve area equals the LVOT area times the ratio of the two VTIs. A narrowed valve makes blood speed up, raising the valve VTI. The LVOT diameter is squared, so small measurement errors in it have a large effect; the VTI ratio avoids that.

Worked example

Defaults: LVOT diameter 2.0 cm; LVOT VTI 20 cm; aortic valve VTI 80 cm; BSA 1.8 m².

CSA = π × 1.0² = 3.14 cm².
AVA = 3.14 × 20 ÷ 80 = 0.79 cm²: Severe (under 1.0 cm²).
Indexed AVA = 0.785 ÷ 1.8 = 0.44 cm²/m²: Severe (under 0.6).
VTI ratio = 20 ÷ 80 = 0.25: Moderate (0.25–0.50) (exactly at the boundary).

Each point is the calculator re-run with only “LVOT diameter (cm)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

LVOT diameter (cm)	Aortic valve area (cm²)
0.5	0.05
1	0.2
1.5	0.44
2	0.79
2.5	1.23
3	1.77
4	3.14

How to read the result

Where does your result fall?

The measures here disagree at the boundary, which is common. Guidelines grade severity from all findings together, including peak velocity, mean gradient, flow status and valve anatomy. When findings conflict, the cardiologist checks measurements and may use further tests.

Common mistakes

Measuring the LVOT diameter in the wrong place or plane.
Misaligning the Doppler beam, which underestimates velocity.
Ignoring low-flow states that make AVA look smaller.
Relying on AVA alone.

Keep in mind: Not a diagnosis. Valve disease is assessed by cardiologists using complete echocardiographic and clinical information.

Frequently asked questions

What aortic valve area is severe?

Under 1.0 cm², or under 0.6 cm²/m² indexed, according to ASE/EACVI 2017.

Why use the VTI ratio?

It avoids squaring the LVOT diameter, the largest source of error.

Can AVA be wrong in low flow?

Yes. Low stroke volume can make the valve open less, so further assessment is needed.

Sources: Baumgartner H, Hung J, Bermejo J, et al., "Recommendations on the echocardiographic assessment of aortic valve stenosis: a focused update from the EACVI and the ASE", J Am Soc Echocardiogr 2017;30(4):372–392

Checked 9 Nov 2026. Baumgartner H, Hung J, Bermejo J, et al., “Recommendations on the echocardiographic assessment of aortic valve stenosis: a focused update from the European Association of Cardiovascular Imaging and the American Society of Echocardiography”, J Am Soc Echocardiogr 2017;30(4):372–392 (continuity equation; Table 3 severity grading).

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