Cardiac Output Calculator – Heart Pumping Capacity
Calculate cardiac output from stroke volume and heart rate
How to Use
- Enter the stroke volume in milliliters (mL)
- Enter the heart rate in beats per minute (bpm)
- Click calculate to see your cardiac output
- Review the interpretation based on normal ranges
What is Cardiac Output?
Cardiac output (CO) is the volume of blood pumped by the heart per minute. It is calculated by multiplying the stroke volume (the amount of blood pumped with each heartbeat) by the heart rate (the number of beats per minute).
The formula is: CO = SV × HR, where SV is stroke volume in milliliters and HR is heart rate in beats per minute. The result is converted to liters per minute by dividing by 1000. Normal cardiac output for adults at rest typically ranges from 4.0 to 8.0 L/min.
Clinical Significance
Cardiac output is a fundamental parameter in cardiovascular physiology and clinical medicine. It reflects the heart's ability to meet the metabolic demands of the body. Decreased cardiac output can lead to inadequate tissue perfusion, while excessive cardiac output may indicate underlying pathology.
| Cardiac Output | Classification | Clinical Implications |
|---|---|---|
| < 3.0 L/min | Critically low | Cardiogenic shock, severe heart failure, requires immediate intervention |
| 3.0 - 4.0 L/min | Low | May indicate heart failure or decreased cardiac function |
| 4.0 - 8.0 L/min | Normal | Adequate cardiac function at rest |
| > 8.0 L/min | High | May indicate hyperdynamic state, exercise, pregnancy, or hyperthyroidism |
Factors Affecting Cardiac Output
Cardiac output is influenced by multiple physiological and pathological factors that affect either stroke volume, heart rate, or both:
- Heart rate: Increased heart rate generally increases cardiac output up to a point (around 160-180 bpm)
- Stroke volume: Determined by preload (venous return), afterload (arterial resistance), and contractility
- Preload: The volume of blood returning to the heart (venous return)
- Afterload: The resistance the heart must overcome to eject blood
- Myocardial contractility: The intrinsic strength of cardiac muscle contraction
- Physical activity: Exercise can increase cardiac output 5-6 times above resting levels
- Body position: Standing reduces cardiac output compared to lying down
- Age: Cardiac output typically decreases with age
Stroke Volume and Heart Rate Relationship
The relationship between stroke volume and heart rate is crucial for understanding cardiac output. While increasing heart rate can increase cardiac output, there's an optimal range. Excessively high heart rates reduce filling time, which decreases stroke volume and ultimately cardiac output.
Average stroke volume for adults at rest is 60-100 mL per beat. Athletes often have higher stroke volumes (100-120 mL) due to cardiac adaptations from training. Average resting heart rate is 60-100 bpm, though well-trained athletes may have resting heart rates as low as 40-60 bpm.
During exercise, cardiac output increases primarily through increased heart rate, with stroke volume increasing moderately. Maximum cardiac output during intense exercise can reach 20-35 L/min in trained athletes, compared to 4-6 L/min at rest.
Frequently Asked Questions
- What is a normal cardiac output?
- Normal cardiac output for adults at rest is 4.0-8.0 L/min. The exact value depends on body size, age, and fitness level. During exercise, cardiac output can increase dramatically to 20-30 L/min or more in trained athletes.
- What does low cardiac output mean?
- Low cardiac output (< 4.0 L/min at rest) may indicate heart failure, cardiogenic shock, severe valve disease, or other cardiac conditions. It means the heart is not pumping enough blood to meet the body's metabolic needs. Very low values (< 3.0 L/min) are critical and require immediate medical attention.
- Can cardiac output be too high?
- Yes, while high cardiac output during exercise is normal, persistently elevated cardiac output at rest (> 8.0 L/min) may indicate conditions such as hyperthyroidism, severe anemia, sepsis, pregnancy, or arteriovenous fistulas. It can also be a compensatory response to metabolic demands.
- How is cardiac output measured in clinical practice?
- Cardiac output can be measured using several methods including thermodilution (using a Swan-Ganz catheter), echocardiography (Doppler ultrasound), impedance cardiography, or Fick method. This calculator provides an estimate based on known or estimated stroke volume and heart rate values.