Stroke volume is the amount of blood the left ventricle ejects with a single heartbeat — the building block that, multiplied by heart rate, gives cardiac output. This guide explains the two standard ways to calculate it, why they should agree, what a normal range looks like, and the three factors that actually drive the number up or down.
Two routes to the same number
Stroke volume (SV) can be derived in more than one way, and this calculator offers the two most common. The direct route is SV = EDV − ESV: subtract how much blood is left in the ventricle right after it contracts from how much was there just before — typically measured by echocardiography. The indirect route rearranges the cardiac-output identity, SV = (CO ÷ HR) × 1000, useful when cardiac output and heart rate are already known (for example from hemodynamic monitoring) but ventricular volumes haven't been measured directly.
For the same patient at the same moment, both methods should return very similar stroke volume values; a substantial disagreement is a signal to recheck the inputs — most often the ventricular-volume measurements, which are more prone to imaging error than a heart-rate reading.
What actually changes stroke volume
Three physiological factors determine stroke volume. Preload is how stretched the ventricular muscle is just before it contracts, driven by how much blood has returned to fill it — reflected directly in EDV. Contractility is the intrinsic strength of the heart muscle's squeeze, independent of how full it started; weakened contractility (as in heart failure) lowers SV even with a normal EDV. Afterload is the resistance the ventricle must pump against to eject blood; high afterload (as in severe hypertension or aortic stenosis) can reduce SV by making ejection harder.
Because SV divided by EDV gives ejection fraction, a low SV with a normal EDV points toward a contractility or afterload problem, while a low SV with a low EDV points toward inadequate filling (reduced preload) instead.
Reading the result against a normal range
A typical resting adult stroke volume is roughly 60–100 mL, though it scales with body size, fitness level, and heart rate. Well-conditioned endurance athletes often show a higher resting SV alongside a lower resting heart rate, which keeps cardiac output normal. SV also varies moment to moment with posture, hydration, and activity — a single reading only tells part of the story.
A stroke volume well under 60 mL, especially alongside a low or normal EDV, can point toward reduced preload, weak contractility, or high afterload, and may warrant further evaluation. This calculator is an educational and screening aid — it does not diagnose or replace direct hemodynamic monitoring by a qualified clinician.