Cardiac Output Formula
Cardiac output measures how much blood the heart pumps per minute.
Learn the CO = HR x SV formula with clinical examples.
The Formula
Cardiac output (CO) is the volume of blood the heart pumps per minute. It is the product of heart rate (how many times the heart beats per minute) and stroke volume (how much blood is pumped per beat).
A typical resting cardiac output for an adult is about 5 liters per minute. During intense exercise, this can increase to 20-25 liters per minute in healthy individuals, and up to 35-40 liters per minute in elite athletes. The body increases cardiac output by raising both heart rate and stroke volume.
Cardiac output is a critical measure in clinical medicine. Abnormally low cardiac output can indicate heart failure, shock, or severe dehydration. The cardiac index (CI = CO / body surface area) normalizes output to body size, allowing meaningful comparisons between patients of different sizes. A normal cardiac index is approximately 2.5-4.0 L/min/m².
Variables
| Symbol | Meaning |
|---|---|
| CO | Cardiac output (in liters per minute, L/min) |
| HR | Heart rate (in beats per minute, bpm) |
| SV | Stroke volume (in milliliters per beat, mL/beat) |
Example 1
A person at rest has a heart rate of 72 bpm and a stroke volume of 70 mL. What is their cardiac output?
Identify the values: HR = 72 bpm, SV = 70 mL/beat
CO = HR × SV = 72 × 70 = 5,040 mL/min
Convert to liters: 5,040 / 1,000
CO = 5.04 L/min
Example 2
During exercise, an athlete's cardiac output increases to 22 L/min with a heart rate of 175 bpm. What is the stroke volume?
Rearrange: SV = CO / HR
Convert CO to mL: 22 L/min = 22,000 mL/min
SV = 22,000 / 175
SV ≈ 125.7 mL/beat
When to Use It
Cardiac output is fundamental to understanding cardiovascular function.
- Assessing heart function in clinical settings
- Monitoring patients in intensive care
- Exercise physiology and athletic performance analysis
- Understanding the effects of medications on the heart