Echocardiography

Cardiac Output & Cardiac Index Calculator

Enter LVOT diameter, LVOT velocity time integral, and heart rate to calculate stroke volume and cardiac output. Add body surface area to obtain cardiac index.

Enter measurements

LVOT diameter

Measure in parasternal long axis during mid-systole. Use the measured diameter; do not assume 2 cm.LVOT VTI

Pulsed-wave Doppler in the apical five-chamber or apical long-axis view.Heart rate

beats/min

Body surface area (optional)

m²

Required for cardiac index and stroke volume index. CO can be calculated without BSA.

Calculated in your browser. Inputs are not saved, added to the URL, or sent by this calculator.

Cardiac output

—L/min

Complete every required field to calculate a result.

LVOT area = π × (diameter / 2)²; SV = LVOT area × VTI; CO = SV × HR / 1000; CI = CO / BSA; SVI = SV / BSA.

Educational use only. This tool and its outputs do not constitute medical advice, diagnosis, or treatment and do not replace clinical judgment. Independently verify the inputs, equations, assumptions, units, and outputs, and confirm that the tool is appropriate for your intended use before relying on a result.

What is cardiac output?

Cardiac output is the volume pumped each minute. Doppler echocardiography estimates forward flow by multiplying LVOT cross-sectional area by the distance traveled by blood during systole, then multiplying by heart rate.

How is it calculated?

LVOT area = π × (diameter / 2)²; SV = LVOT area × VTI; CO = SV × HR / 1000; CI = CO / BSA; SVI = SV / BSA.

How to measure LVOT diameter and VTI

Measure LVOT diameter in the parasternal long-axis view during mid-systole, with the aortic valve open. It is often around 2 cm in adults, but use the patient's measured value: diameter is squared in the calculation.

Obtain LVOT VTI using pulsed-wave Doppler in the apical five-chamber or apical long-axis view, aligning the beam with outflow and sampling just proximal to the aortic valve. Trace the systolic spectral envelope on the machine or with appropriate offline software.

VTI is a stroke distance, expressed in centimeters. Values around 15–25 cm are commonly encountered, but depend on loading conditions, rhythm, and physiology. They are an orientation rather than a universal normal range.

Worked example: LVOT 2.2 cm, VTI 20 cm, heart rate 75

With an LVOT diameter of 2.2 cm, area = π × (2.2 / 2)² ≈ 3.80 cm². At a VTI of 20 cm, stroke volume is approximately 76.0 mL/beat. At 75 beats/min, cardiac output is approximately 5,702 mL/min, or 5.70 L/min.

If BSA is 1.9 m², cardiac index is approximately 3.00 L/min/m². The calculator retains full precision until display; rounding intermediate steps can slightly change the result.

Watch: how to acquire LVOT measurements

POCUS 101: acquiring the apical five-chamber view and measuring LVOT VTI ↗

The accompanying step-by-step acquisition guide ↗ covers parasternal LVOT diameter measurement, apical five-chamber acquisition, pulsed-wave Doppler placement, and tracing the VTI.

Clinical interpretation

Diameter and VTI in centimeters yield stroke volume in cm³, equivalent to mL. Dividing mL/min by 1000 gives CO in L/min. Cardiac index adjusts CO for body size and is reported in L/min/m². A single value does not establish perfusion adequacy or identify a treatment.

Clinical considerations

Diameter error is amplified because the value is squared. Accurate sample placement and Doppler alignment matter; aortic-valve VTI is not interchangeable with LVOT VTI.

Use representative beats and an appropriate averaging strategy for irregular rhythms. Severe regurgitation, shunts, outflow obstruction, and poor image quality can make LVOT forward flow differ from effective systemic flow.

BSA is optional for CO and required for index calculations. This tool accepts BSA directly; it does not infer body size or a default diameter.

Common questions

Can I calculate cardiac index without BSA?

No. Cardiac index is cardiac output divided by body surface area. Stroke volume and CO can still be calculated without BSA.

Is LVOT VTI measured in cm or cm/s?

VTI is measured in cm. It integrates blood velocity over systolic time and represents a distance.

References

These calculators are educational tools. Their outputs do not constitute medical advice and do not replace clinical judgment.