Formula & Calculator
Cardiac Output
The amount of blood your heart pumps per minute, calculated from stroke volume and heart rate.
Interpretation
CO = SV × HR. The volume of blood pumped by the heart per minute. Used to assess cardiovascular function and guide therapy in critical care.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| CO | Cardiac output | L/min |
| SV | Stroke volume | mL |
| HR | Heart rate | beats/min |
What it means
Cardiac output (CO) is the total volume of blood ejected by the left ventricle per minute. It is the product of stroke volume (SV) and heart rate (HR). CO is a key determinant of oxygen delivery to tissues. It is measured in litres per minute. In critical care, CO is monitored to guide fluid administration, drug therapy, and to assess response to interventions. It is also used in exercise physiology to evaluate fitness. Understanding CO is fundamental for cardiovascular physiology and for managing patients with heart failure or shock.
Worked example
Cardiac Output – Two Detailed Examples
Real‑World| Parameter | Value |
|---|---|
| SV (mL) | 70 |
| HR (bpm) | 70 |
| Parameter | Value |
|---|---|
| SV | 90 |
| HR | 50 |
Common mistakes
- Cardiac output: CO = SV × HR – the volume of blood pumped per minute.
- Stroke volume (SV): The volume of blood ejected with each beat – in mL/beat.
- Heart rate (HR): Beats per minute.
- Units: CO in mL/min (or L/min if divided by 1000).
- Normal resting CO: ~5 L/min.
Applications
Cardiac output (CO = SV × HR) is the volume of blood pumped by the heart per minute, a critical measure of cardiovascular function. Clinicians use CO to assess cardiac performance in intensive care, during surgery, and in heart failure management. It guides fluid resuscitation, vasopressor therapy, and inotropic support. By understanding CO, healthcare providers can optimise perfusion to tissues and prevent organ failure. This formula is also used in exercise physiology to study fitness adaptations. Measuring CO non‑invasively is increasingly common, making this calculation a standard part of haemodynamic monitoring.
- Haemodynamic monitoring in critical care and anaesthesia
- Heart failure management and therapy titration
- Exercise physiology and cardiovascular fitness assessment
- Shock diagnosis and fluid resuscitation guidance
- Research on cardiovascular physiology and disease
Frequently Asked Questions
It calculates the amount of blood the heart pumps per minute: CO = SV × HR, where SV is stroke volume (mL) and HR is heart rate (beats/min).
SV = stroke volume – the volume of blood pumped per beat (mL)
HR = heart rate (beats per minute)
At rest, CO is typically 4–8 L/min. It can increase to >20 L/min during exercise.
A person has SV = 70 mL and HR = 70 bpm. CO = 70 × 70 = 4900 mL/min = 4.9 L/min.
- Forgetting to convert stroke volume from mL to L (should divide by 1000).
- Using average values without accounting for individual variation.
Both SV and HR increase, so CO rises, sometimes to 20–30 L/min in athletes.
Preload (venous return), afterload (arterial resistance), and contractility.
Blood pressure = CO × total peripheral resistance. An increase in CO tends to raise pressure.
Echocardiography, thermodilution (Swan‑Ganz catheter), or Doppler ultrasound.
An alternative method: CO = oxygen consumption / (arterial‑venous oxygen difference).