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Cardiac output is the volume of blood ejected by one ventricle per minute.
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Formula
CO in L/min · HR in beats/min · SV in mL/beat; convert units before multiplication
| Symbol | Meaning | Unit |
|---|---|---|
| Cardiac output per ventricle | L/min | |
| Heart rate | beats/min | |
| Stroke volume per heartbeat | mL/beat |
\dot Q=HF\cdot SVThis is a volume balance: beats per time multiplied by volume per beat yields volume per time. In a steady closed circulation, both ventricles pump the same mean flow. The equation describes flow, not by itself organ perfusion or a diagnosis.
Instantaneous or interval-mean flow when HR and SV refer to the same period.
Volume per beat times beats per minute gives volume per minute.
Solve for a quantity
Heart rate and volume must refer to the same ventricle and period.
HR=80/min and SV=65 mL: calculate cardiac output.
80·65=5,200 mL/min=5.2 L/min.
Reporting mL as L.
Divide mL/min by 1,000; beats cancel.
Formula cluster
The product describes flow, not tissue perfusion by itself.
At HR=70/min and SV=70 mL/beat, CO=4,900 mL/min=4.9 L/min. Check: beats/min multiplied by mL/beat cancels beats and leaves volume/time.
Basic cardiovascular physiology and the relation between heart rate and stroke volume
Here is how to work through a typical Cardiac output (HZV = HF · SV) task step by step:
Task
HR=80/min and SV=65 mL: calculate cardiac output.
Solution path
80·65=5,200 mL/min=5.2 L/min.
Multiply heart rate in beats per minute by stroke volume in milliliters per beat. At 70/min and 70 mL/beat, the result is 4,900 mL/min or 4.9 L/min. The beat unit cancels; convert to liters by dividing by 1,000. Heart rate and stroke volume must refer to the same interval, otherwise the calculated flow combines mismatched measurements. The equation gives only volume flow. It replaces neither tissue-perfusion measurement nor clinical assessment and requires matched HR and SV measurements. Conditions such as exercise or rest matter for interpretation.
The product equation gives the calculation, not the physiological regulation. A changed rate can alter filling time and therefore stroke volume; preload, afterload, contractility, venous return and autonomic control also interact. Increasing heart rate therefore does not automatically raise output in direct proportion. The formula is a balance relation and alone explains neither the cause nor clinical meaning of a measured change. The equation gives only volume flow. It replaces neither tissue-perfusion measurement nor clinical assessment and requires matched HR and SV measurements. Conditions such as exercise or rest matter for interpretation.
Cardiac output is blood flow per time and thus one component of oxygen transport to tissues. Oxygen delivery also depends on blood oxygen content; high flow with low hemoglobin can mean something different from the same flow with normal content. Output alone does not measure how much oxygen a particular tissue extracts. Content measurements and further balance quantities are needed for that. The equation gives only volume flow. It replaces neither tissue-perfusion measurement nor clinical assessment and requires matched HR and SV measurements. Conditions such as exercise or rest matter for interpretation.
Reproduce the example calculation: At HR=70/min and SV=70 mL/beat, CO=4,900 mL/min=4.9 L/min. Cardiac output uses HZV = HF · SV. In plain terms, cardiac output is the volume of blood ejected by one ventricle per minute. Unit check: CO in L/min · HR in beats/min · SV in mL/beat; convert units before multiplication. Instantaneous or interval-mean flow when HR and SV refer to the same period. Values are comparable only when their definitions, denominators and periods match. Record these details next to the result so the reference group is clear. If the direction is implausible, check data preparation and the calculation basis before discussing biological causes.
A key limit of Cardiac output is this: Instantaneous or interval-mean flow when HR and SV refer to the same period. Do not use the metric without its reference; it is useful for Basic cardiovascular physiology and the relation between heart rate and stroke volume. Cardiac output is the volume of blood ejected by one ventricle per minute. When comparing populations or experiments, check whether definitions, denominators and observation periods match. If the assumption is implausible, the result shows only what the simplified model calculates from its inputs; it is not a reliable estimate for the target population. State this limitation in the report, and do not infer a causal effect from the formula alone.
Quanta exam set
Curated exam set for "Cardiac output":
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Which formula describes Cardiac output?
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How do you rearrange Cardiac output for Solve for a quantity?
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Which common mistake happens with Cardiac output?
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