Doppler Echo Cardiac Output Calculator (LVOT diameter × VTI × heart rate)

Understanding the Doppler echo cardiac output calculator — concept and principle

This calculator estimates stroke volume and cardiac output from three echocardiography measurements: the diameter of the left ventricular outflow tract (LVOT), the velocity-time integral (VTI) of blood flow in it, and the heart rate. Clinicians use it to assess heart function, judge fluid responsiveness and check valve calculations.

Flow = area × distance: with the default inputs the result is 4.4 L/min (× 70 bpm ÷ 1,000).

How it is calculated

LVOT area (cm²) = π × (D ÷ 2)² = 0.785 × D²

Stroke volume (mL) = LVOT area × VTI

Cardiac output (L/min) = stroke volume × heart rate ÷ 1,000

Cardiac index = cardiac output ÷ body surface area; stroke volume index = stroke volume ÷ body surface area

D is the LVOT diameter in cm, measured in mid-systole from inner edge to inner edge.
VTI is traced from the pulsed-wave Doppler signal in the LVOT, in cm.
Enter a body surface area of 0 to skip the indexed values.

The principle

Flow through a tube equals its cross-sectional area times the distance the fluid travels. The VTI is the area under the velocity curve during one beat, which is the distance a column of blood moves in that beat, sometimes called the stroke distance. Multiplying that distance by the area of the outflow tract gives the volume ejected per beat, assuming the tract is circular and the flow is evenly spread across it. Multiplying by the heart rate turns volume per beat into volume per minute.

Worked example

Default inputs: D 2.0 cm, VTI 20 cm, heart rate 70 bpm, body surface area 1.8 m².

LVOT area = π × 1.0² = 3.14 cm².
Stroke volume = 3.1416 × 20 = 62.8 mL, shown as 63 mL.
Cardiac output = 62.83 × 70 ÷ 1,000 = 4.4 L/min.
Cardiac index = 4.398 ÷ 1.8 = 2.44 L/min/m².
Stroke volume index = 62.83 ÷ 1.8 = 35 mL/m².

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)	Cardiac output (L/min)
0.5	0.27
1	1.1
1.5	2.47
2	4.4
2.5	6.87
3	9.9
4	17.59

How to read the result

Where does your result fall?

Cardiac output in a resting adult is commonly around 4–8 L/min, and a resting cardiac index of roughly 2.5–4 L/min/m² is often quoted as normal. Indexing to body size makes small and large patients comparable.

Common mistakes

Measuring the diameter at the wrong level or outer edges. Because D is squared, a 1 mm error changes the result by about 10%.
Placing the sample volume where the Doppler angle is poor, which underestimates VTI.
Using a single beat in atrial fibrillation. Average several beats.

Keep in mind: This is an estimate for trained clinicians to read with the rest of the echocardiogram, not a diagnosis. The circular-tract assumption and measurement errors limit its accuracy.

Frequently asked questions

What is a normal LVOT VTI?

Many references quote about 18–22 cm in adults at rest, but values depend on heart rate and body size.

Why is VTI alone sometimes used?

The LVOT diameter rarely changes in one patient, so changes in VTI track changes in stroke volume without the error of squaring the diameter.

Is echo cardiac output as accurate as thermodilution?

It agrees reasonably on average but individual readings can differ, mainly because of the diameter measurement.

Sources: Baumgartner H et al., "Echocardiographic assessment of valve stenosis: EAE/ASE recommendations for clinical practice", Eur J Echocardiogr 2009;10:1–25 · Zoghbi WA et al., "Recommendations for noninvasive evaluation of native valvular regurgitation", J Am Soc Echocardiogr 2017;30:303–371

Checked 9 Nov 2026. Baumgartner H, Hung J, Bermejo J, et al., “Echocardiographic assessment of valve stenosis: EAE/ASE recommendations for clinical practice”, Eur J Echocardiogr 2009;10:1–25 (CSA_LVOT = π(D/2)², flow = CSA × VTI); Zoghbi WA et al., ASE “Recommendations for noninvasive evaluation of native valvular regurgitation”, J Am Soc Echocardiogr 2017;30:303–371 (SV = 0.785 × d² × VTI).

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