Cardiac output- Definition, formula, factors

Cardiac output

The volume of blood expelled from the heart’s left ventricle into the systemic circulation is measured by the heart’s pumping rate, or cardiac output (CO). It is a basic physiological metric that shows how well the heart functions overall in providing oxygen and nutrients to the body’s tissues and organs.

Cardiac output formula

The formula for calculating cardiac output (CO) is:


  • Heart Rate (HR): The number of heartbeats per minute.
  • Stroke Volume (SV): The volume of blood ejected by the left ventricle of the heart with each contraction.

So, cardiac output is the product of heart rate and stroke volume, representing the amount of blood pumped by the heart per unit of time (usually measured in liters per minute). This formula is fundamental in understanding cardiovascular physiology and is commonly used in clinical settings to assess cardiac function and circulation.

Cardiac output factors

Cardiac output is influenced by various factors that affect both heart rate (HR) and stroke volume (SV). The formula for cardiac output (CO) is . Here are some of the key factors affecting cardiac output:

  1. Heart Rate (HR):

    • Autonomic Nervous System: The sympathetic nervous system tends to increase heart rate, while the parasympathetic nervous system has the opposite effect.
    • Hormones: Certain hormones, such as epinephrine (adrenaline) and norepinephrine, can increase heart rate.
    • Fitness Level: Regular exercise and cardiovascular fitness can lower resting heart rate.
  2. Stroke Volume (SV):

    • Preload: The volume of blood in the ventricles before contraction. An increase in preload can lead to an increase in stroke volume.
    • Afterload: The resistance the heart must overcome to eject blood into the systemic circulation. Increased afterload can reduce stroke volume.
    • Contractility: The force of ventricular contraction. An increase in contractility can lead to an increase in stroke volume.
    • End-Diastolic Volume (EDV): The volume of blood in the ventricles at the end of diastole. It is related to preload and affects stroke volume.
  3. Venous Return:

    • The amount of blood returning to the heart from the veins. An increase in venous return typically leads to an increase in stroke volume and, consequently, cardiac output.
  4. Blood Volume:

    • The overall volume of blood in the circulatory system. Changes in blood volume can affect preload and, consequently, stroke volume and cardiac output.
  5. Body Position:

    • Changes in body position, such as moving from a lying down to a standing position, can affect venous return and, subsequently, cardiac output.
  6. Age and Gender:

    • Cardiac output may vary with age and gender. For example, the maximum heart rate tends to decrease with age.
  7. Pathological Conditions:

    • Various cardiac and non-cardiac conditions, such as heart failure, valvular disorders, and anemia, can significantly impact cardiac output.

Understanding these factors is crucial in assessing and managing cardiovascular health. Clinicians often consider these variables when evaluating patients and devising appropriate treatment plans.

Cardiac output conclusion

To sum up, cardiac output is an important physiological measure that shows how well the heart pumps blood to satisfy the body’s metabolic needs. It is measured in liters per minute and is derived from the product of heart rate (HR) and stroke volume (SV).

The autonomic nervous system, hormone control, fitness level, preload, afterload, contractility, venous return, blood volume, body posture, age, gender, and a number of pathological diseases are some of the variables that affect cardiac output. Any of these elements changing can affect how well the heart pumps blood.

In order to evaluate the response to therapies, guide treatment decisions, and measure cardiovascular health, cardiac output monitoring is crucial in clinical settings. Deviations from normal cardiac output levels highlight the significance of comprehending and controlling these elements in healthcare, as they might point to a variety of cardiovascular illnesses or other medical issues.

Overall, cardiac output is an important metric in the evaluation of cardiovascular health and general physiological well-being because it offers insightful information about the dynamic interactions between the heart and the circulatory system.

Scroll to Top