Cardiac output (CO) is the volume of blood pumped by the heart per minute, calculated as the product of heart rate (HR) and stroke volume (SV). It's the most fundamental measure of cardiac performance and is central to assessing heart failure, shock, and exercise capacity. Our cardiac output calculator computes CO in L/min and the cardiac index (CO ÷ body surface area) in L/min/m², the body-size-normalized version that's more useful for clinical comparisons.
Input resting or measured heart rate in bpm.
Provide stroke volume per beat in mL (typically 60-100).
Add body surface area for cardiac index.
Review cardiac output and category.
Cardiac output equals heart rate times stroke volume. A typical resting adult: 70 bpm × 70 mL = 4,900 mL/min ≈ 4.9 L/min. During peak exercise it can rise to 20-25 L/min in trained athletes. Cardiac index normalizes for body size — normal range 2.5-4.0 L/min/m².
CO = HR × SV / 1000 • CI = CO / BSA
Normal resting CO: 4-8 L/min for healthy adults
Cardiac index 2.5-4.0 L/min/m² is the body-size-normalized normal range
Peak exercise CO can reach 20-25 L/min in trained endurance athletes
Low CO with normal HR suggests low stroke volume — possible heart failure
High CO is normal during exercise, fever, hyperthyroidism, or pregnancy
CO can be measured directly via thermodilution (Swan-Ganz) or estimated via echocardiography
Cardiac output is one of the most critical hemodynamic parameters in clinical medicine, representing the total volume of blood the heart pumps per minute. Normal resting cardiac output ranges from 4 to 8 liters per minute in adults, calculated as the product of heart rate and stroke volume. Clinicians monitor cardiac output to assess heart failure severity, guide fluid resuscitation in sepsis, manage critically ill patients in the ICU, and evaluate the effectiveness of vasoactive medications. The cardiac index — cardiac output normalized to body surface area — provides a size-adjusted measure that allows meaningful comparisons between patients of different body sizes. A cardiac index below 2.2 L/min/m-squared typically indicates cardiogenic shock, while values above 4.0 may suggest a hyperdynamic state seen in early sepsis or thyrotoxicosis. This cardiac output calculator computes CO from heart rate and stroke volume, derives cardiac index using the Du Bois body surface area formula, calculates stroke volume index, and classifies the hemodynamic profile. It serves as a rapid bedside reference for nurses, medical students, and clinicians interpreting hemodynamic data.
Cardiac output is the most direct measure of how much blood the heart delivers to the body each minute. Every clinical assessment of heart failure, shock, and exercise capacity ultimately comes back to CO. It's also the framework for understanding why treatments work — increasing HR, increasing contractility, or reducing afterload all improve CO via different mechanisms.
Cardiac output equals heart rate multiplied by stroke volume, so CO = HR x SV. If your heart beats 70 times per minute and ejects 70 mL of blood per beat, that is 4,900 mL/min, or roughly 4.9 L/min.
The formula reveals the two independent levers the body uses to change blood delivery. Raising heart rate (beats per minute) or stroke volume (milliliters ejected each beat) both increase output.
Three factors drive the equation:
The American Heart Association describes this same relationship when explaining how the heart adapts to demand. Because stroke volume is measured in mL, the calculator divides by 1,000 to report CO in liters per minute.
Enter your heart rate and stroke volume, and the calculator returns cardiac output in L/min instantly. Add body surface area to also compute cardiac index.
Work through a resting adult example:
The result is 70 x 70 = 4,900 mL/min, or 4.9 L/min. Dividing by BSA gives a cardiac index of about 2.58 L/min/m squared, which falls in the normal resting band.
Stroke volume typically runs 60 to 100 mL in healthy adults, so use a measured echocardiography value when you have one. If you only know heart rate, pair this tool with a stroke volume estimate rather than guessing. The National Heart, Lung, and Blood Institute (NHLBI) notes that accurate hemodynamic inputs matter far more than the arithmetic itself.
Normal resting cardiac output for a healthy adult is roughly 4 to 8 liters per minute. The corresponding cardiac index generally sits between 2.5 and 4.0 L/min/m squared.
These ranges shift with age, fitness, and body size. A small older adult and a large young athlete can both be perfectly normal at very different absolute CO values, which is exactly why clinicians favor the size-adjusted cardiac index.
Several conditions predictably move output outside the resting band:
The Centers for Disease Control and Prevention (CDC) and the American Heart Association both emphasize that a single number is only meaningful alongside symptoms and context, not in isolation.
Cardiac index is cardiac output divided by body surface area, giving a size-adjusted number that compares fairly across patients. Normal cardiac index is about 2.5 to 4.0 L/min/m squared.
Raw cardiac output can mislead. A CO of 5 L/min looks reassuring, but in a very large person it may actually be low once normalized. Dividing by BSA removes that body-size distortion.
Clinicians lean on cardiac index for critical decisions:
This calculator uses a standard body surface area formula to derive the index. The American Heart Association and NHLBI both treat cardiac index as the more clinically actionable metric when comparing hearts of different sizes.
Low cardiac output means the heart is not delivering enough blood to meet the body's metabolic needs. When output falls, organs receive less oxygen and warning symptoms appear.
Common causes trace back to a problem with rate, filling, or squeeze strength:
Typical symptoms include fatigue, shortness of breath, cool or pale extremities, dizziness, and confusion. If heart rate is adequate but output is still low, the stroke volume is usually the culprit.
The National Heart, Lung, and Blood Institute (NHLBI) and the American Heart Association stress that persistent low-output symptoms warrant prompt medical evaluation. This calculator is an educational reference and does not replace bedside assessment, echocardiography, or a clinician's judgment.
High cardiac output is often a normal, healthy response rather than a disease. During exercise, fever, pregnancy, or anxiety, the body deliberately raises output to deliver more oxygen.
A sustained high-output state at rest, however, can point to an underlying condition. The heart is working hard to compensate for low vascular resistance or increased metabolic demand.
Recognized drivers of elevated resting output include:
Sustained high output can eventually strain the heart, a scenario clinicians call high-output heart failure. The American Heart Association notes that treatment targets the underlying cause rather than the output number itself. Use this calculator to quantify the value, then interpret it against the person's clinical picture and history.
During intense exercise, cardiac output can climb from about 5 L/min at rest to 20 to 25 L/min in trained endurance athletes. Untrained adults typically peak nearer 14 to 18 L/min.
Both levers of the formula rise together. Heart rate accelerates while stroke volume increases as the ventricle fills and empties more completely.
Training reshapes these numbers over time:
The American College of Sports Medicine (ACSM) links this expanded output capacity to improved aerobic performance. The CDC recommends regular aerobic activity for cardiovascular health. Enter an elevated heart rate and stroke volume above to see how output scales during effort compared with rest.
Clinicians measure cardiac output using thermodilution, the Fick principle, or echocardiography rather than a bedside formula alone. Each method estimates the same value through different physics.
The main techniques differ in invasiveness and setting:
Invasive monitoring is generally reserved for critically ill patients in the ICU, while echocardiography is common in outpatient cardiology. This calculator reproduces the underlying HR-times-SV arithmetic so you can check or teach the concept.
The National Heart, Lung, and Blood Institute (NHLBI) and the American Heart Association describe these measurement approaches in their clinical education materials. A calculated estimate should always be confirmed against a validated clinical measurement before guiding treatment.
The most common mistake is mixing up units, entering stroke volume in liters instead of milliliters. A value of 70 mL is correct; typing 0.07 or 70,000 throws the result off by orders of magnitude.
Watch for these frequent errors:
Another pitfall is assuming a normal CO rules out disease; the heart can maintain output by overworking until it decompensates. The American Heart Association cautions against interpreting any one hemodynamic value in isolation. Double-check your inputs, confirm the units, and treat this calculator as an educational cross-check rather than a diagnostic device.
Cardiac output is blood pumped per minute, stroke volume is blood pumped per beat, and ejection fraction is the percentage of ventricular blood ejected each beat. They are related but not interchangeable.
The distinctions matter for interpreting a heart report:
A person can have a normal ejection fraction yet reduced cardiac output if heart rate or filling is impaired, which is why heart failure with preserved ejection fraction exists. The American Heart Association and NHLBI treat these three metrics as complementary pieces of one hemodynamic picture. Use this calculator for output and index, and read them alongside a measured ejection fraction from echocardiography.
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All formulas verified against official standards.