Article — Stroke Volume Calculator
Stroke Volume Calculator
Stroke volume is the amount of blood the left ventricle pumps in a single beat — typically 60-100 mL in a resting adult, calculated as SV = EDV - ESV. Combined with heart rate it gives cardiac output, the body's master indicator of circulatory function.
The metric goes back to William Harvey, who in 1628 first argued that the heart was a pump, not a furnace. Modern cardiology uses three derived numbers — stroke volume, cardiac output and ejection fraction — to grade heart performance in every clinical setting from intensive care to sports medicine.
What is stroke volume?
Stroke volume is the volume of blood the left ventricle ejects with each heartbeat, measured in millilitres. In a typical 70 kg adult at rest, the left ventricle fills to about 120 mL at end-diastole and contracts down to about 50 mL at end-systole. The 70 mL that left is the stroke volume.
The number matters because every tissue in the body depends on the blood that gets pumped out. A low stroke volume means kidneys, muscles and brain receive less oxygen per beat, and the body usually compensates by raising heart rate — which works until it cannot.
The left ventricle of an elite endurance athlete can pump 180 mL per beat — nearly three times a sedentary adult. That is why a trained cyclist can maintain a resting heart rate near 40 bpm while still delivering normal cardiac output.
The stroke volume formula
The defining equation is simple subtraction. End-diastolic volume (EDV) is the blood in the ventricle at peak filling. End-systolic volume (ESV) is what is left after contraction. The difference is stroke volume.
SV = EDV - ESV mL per beatCO = SV × HR ÷ 1000 L per minuteEF = SV ÷ EDV × 100 %Echocardiography is the workhorse for measuring EDV and ESV non-invasively. The sonographer captures two-dimensional images of the ventricle at peak filling and peak contraction, then traces the chamber border to compute volumes. Modern 3D probes and cardiac MRI give more accurate numbers — MRI is the reference standard — but cost limits routine use.
Stroke volume vs. cardiac output
Stroke volume describes a single beat. Cardiac output describes a minute of beats. The link is heart rate: cardiac output equals stroke volume times heart rate, divided by 1,000 to convert mL/min into L/min. A resting heart at SV 70 mL and HR 70 bpm produces 4.9 L/min — enough to circulate the body's entire 5 L of blood every minute.
The relationship is not linear, though. Above a heart rate of roughly 150 bpm, diastolic filling time shrinks so much that EDV falls and stroke volume follows it down. This is why a tachycardia of 180 bpm in atrial fibrillation can produce a lower cardiac output than a normal sinus rhythm at 70 bpm — the heart is too busy beating to fill properly.
Stroke volume and ejection fraction
Ejection fraction is stroke volume expressed as a percent of EDV. It answers a different question: not how much blood was ejected, but how completely the ventricle emptied. A 70 mL stroke volume from a 120 mL ventricle (EF 58%) reflects healthy mechanics. The same 70 mL from a 200 mL dilated ventricle (EF 35%) signals heart failure with reduced ejection fraction.
The AHA and ACC divide patients by EF: below 40% is HFrEF, 40-49% is HFmrEF (mid-range), and 50%+ with symptoms is HFpEF (preserved). Treatment differs sharply between groups, which is why this percentage is the most influential cardiac number in modern cardiology.
Normal stroke volume ranges
- Resting adult = 60-100 mL (average ~70 mL)
- Endurance athlete, rest = 100-130 mL
- Healthy adult, maximal exercise = 120-140 mL
- Elite athlete, maximal exercise = 160-180 mL
- Heart failure, rest = 40-60 mL
- Pediatric (5-12 y) = 25-50 mL — scale with body surface area
- Cardiac index target = 2.5-4.0 L/min/m²
- Stroke volume index = 35-65 mL/m²
What affects stroke volume
Three classical determinants drive stroke volume: preload, afterload and contractility. Preload is how much blood arrives at the ventricle (driven by venous return and intravascular volume). Afterload is the resistance the ventricle has to push against (driven by arterial pressure and aortic stiffness). Contractility is the intrinsic squeeze strength of the cardiac muscle itself.
Frank-Starling's law explains why athletes have high stroke volumes: their ventricles stretch further during filling, generating a stronger contraction the next beat. Strength training does not produce the same effect — only endurance training meaningfully grows EDV.
Drugs hit each lever in turn. Beta-blockers reduce contractility and heart rate (lowering oxygen demand). ACE inhibitors and ARBs lower afterload. Diuretics lower preload. Inotropes like dobutamine raise contractility for short-term rescue in shock. The stroke volume calculator can be used to gauge how a drug change is expected to shift the numbers before the next echo.
Stroke volume in heart failure
In HFrEF, the ventricle is dilated and weak: EDV is high, contractility is low, ejection fraction crashes below 40%, and stroke volume usually falls to 40-60 mL. The body compensates with sympathetic activation (faster heart rate) and renal sodium retention (more preload). Both compensations work in the short term and become harmful in the long term — the classic neurohormonal trap.
This calculator is an educational tool. Stroke volume estimates do not replace echocardiography or clinical examination. Symptoms of heart failure — breathlessness, leg swelling, sudden weight gain, fatigue — require evaluation by a clinician. Call emergency services for chest pain or sudden, severe shortness of breath.
Common stroke volume mistakes
The most frequent error is conflating stroke volume with ejection fraction. A patient can have a normal EF but a low stroke volume if the ventricle is small (restrictive cardiomyopathy, severe hypovolemia, cardiac tamponade). The opposite is also true — dilated cardiomyopathy can produce a near-normal stroke volume despite a low EF, because EDV is enlarged.
Operator-dependent echo measurement is the second source of error. EDV and ESV depend on the imaging plane and on whether the tracer captures the true endocardial border. Inter-observer variability of 10-15% is normal, which is why serial measurements use the same sonographer when possible. The American Society of Echocardiography publishes specific protocols (the biplane disk summation, often called Simpson's method) to reduce this drift.