π Stroke Volume Calculator
How much blood each heartbeat ejects.
Stroke volume
For informational purposes only, not medical advice.
Stroke volume is the milliliters of blood ejected per heartbeat, normally 50 to 100 mL. From cardiac output and heart rate it is simply output divided by rate: 5.0 L/min at 70 beats per minute gives 71.4 mL per beat. From echocardiography it is the LVOT cross-sectional area times the velocity-time integral, the same volume measured directly at the aortic valve.
Cardiac output gets the headlines, but stroke volume is the more sensitive variable: output can look normal while a fast heart rate masks a failing stroke volume. That is why the number matters in heart failure, shock, and valve disease.
How to Use This Calculator
Pick the method that matches your data. The cardiac output method needs a measured or estimated output; the echo method needs the LVOT diameter and VTI from the echo report.
Choose the method tab. Use cardiac output plus heart rate for bedside estimates, or the echo method when you have the measurements.
Enter cardiac output in L/min and heart rate, or LVOT diameter in cm and VTI in cm from the echo.
Read the stroke volume in mL with the normal-range interpretation. Values under 50 suggest the heart is struggling per beat.
The Two Formulas
The output method is arithmetic: 5 liters a minute divided among 70 beats. The echo method is geometry: the LVOT is treated as a circle, its area times the distance blood travels per beat (the VTI) equals the volume ejected. Both should agree within 10 to 15 percent; larger gaps mean one of the inputs is off, usually the diameter, since area squares its error.
Multiply stroke volume by heart rate and you are back at cardiac output, which makes the trio self-checking. If the echo SV times the heart rate does not roughly equal the measured output, remeasure before acting.
Worked Example
Cardiac output 5.0 L/min, heart rate 70: convert output to 5,000 mL/min and divide by 70 beats, giving 71.4 mL per beat, comfortably normal. Now the echo cross-check: LVOT diameter 2.0 cm gives an area of 3.14 cm2, times a VTI of 22 cm gives 69.1 mL, agreeing within a few percent.
That agreement is the useful part. When the two methods converge near 70 mL, you can trust the number. When they diverge, say 45 by one and 80 by the other, the honest answer is that something was mismeasured, and the diameter is the usual suspect.
Reading Your Result
| Stroke volume | Meaning |
|---|---|
| Under 50 mL | Low. Consider reduced contractility, severe valve disease, or underfilling. |
| 50 to 100 mL | Normal resting range for adults. |
| Over 100 mL | High. Seen in athletic hearts, anemia, hyperthyroidism, or measurement error. |
My take: always read stroke volume next to heart rate. An SV of 45 at a heart rate of 110 still delivers nearly 5 L/min, which is why tachycardia compensates, and why losing that compensation, for example with a beta blocker in a failing heart, can drop output fast.
Limits
The output method inherits every error in the cardiac output measurement, and thermodilution outputs wobble. The echo method assumes a circular LVOT and a clean VTI tracing; arrhythmias make both beat-to-beat variable. Indexing to body surface area (stroke volume index, normal 33-47 mL/m2) refines interpretation in very small or large patients, which this page leaves out for simplicity.
Related Tools
Heart rate drives the math, so the max heart rate calculator and heart rate zone calculator frame the rate side. The blood pressure checker adds the pressure the volume generates.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is stroke volume?
The volume of blood the left ventricle ejects per heartbeat, normally 50 to 100 mL at rest. It equals cardiac output divided by heart rate, or on echo, the LVOT area times the velocity-time integral.
How do you calculate stroke volume from cardiac output?
Divide cardiac output by heart rate with matched units: 5 L/min is 5,000 mL/min, divided by 70 bpm gives about 71 mL per beat. The units must agree or the answer is off by a thousand.
What is the LVOT VTI method?
Echocardiography measures the left ventricular outflow tract diameter and the velocity-time integral of flow through it. Stroke volume equals pi times (diameter/2) squared times VTI. It is the standard noninvasive method.
What is a normal stroke volume?
50 to 100 mL per beat at rest in adults. Indexed to body surface area, normal is roughly 33 to 47 mL per square meter. Athletes and larger people run higher.
What causes low stroke volume?
Weak contraction (heart failure), severe aortic stenosis or mitral regurgitation, underfilling from dehydration or bleeding, and cardiac tamponade. The cause determines the treatment, so low SV triggers a workup, not a single fix.
What is the difference between stroke volume and cardiac output?
Stroke volume is per beat; cardiac output is per minute, equal to stroke volume times heart rate. Output can stay normal while stroke volume falls if heart rate rises to compensate.
Can stroke volume be too high?
Unusually high values occur in high-output states like anemia, hyperthyroidism, pregnancy, and arteriovenous shunts, or from overestimated LVOT diameter on echo. Persistent elevation deserves evaluation.
Why do the two methods sometimes disagree?
Usually LVOT diameter error, since area squares it: a 2 mm overread inflates volume substantially. Arrhythmia, poor VTI tracings, and thermodilution noise also contribute. Agreement within 15 percent is good.
Does heart rate affect stroke volume?
Inversely at extremes: very fast rates cut filling time and lower stroke volume, while trained slow hearts fill longer and eject more per beat. The product of the two, cardiac output, is what the body defends.
Who should interpret stroke volume results?
A clinician with the full hemodynamic picture. Echo-derived values belong in the cardiology or ICU context where they were measured. This calculator teaches the math behind the number.