Cardiac Output Equation

What is cardiac output?

Cardiac output is the volume of blood the heart pumps per minute and is a fundamental indicator of overall cardiac function (King & Lowery, 2023). It is calculated using the formula: stroke volume multiplied by heart rate. Stroke volume refers to the amount of blood ejected by the left ventricle with each heartbeat (ScienceDirect, 2018), and when combined with the number of beats per minute, it provides the cardiac output measurement in liters per minute (L/min). Normal cardiac output ranges between 4 to 8 L/min in a healthy adult at rest.

Determining cardiac output is essential for evaluating blood flow, blood pressure, and the delivery of oxygen-rich blood and nutrients throughout the body. It also helps assess whether the heart pumps efficiently under various physiological conditions. Clinicians may measure cardiac output invasively or non-invasively using pulmonary artery catheterization, which samples venous blood. It also calculates cardiac index, which adjusts cardiac output to body surface area for a more individualized assessment.

How do you calculate cardiac output?

Cardiac output refers to the amount of blood the heart pumps in one minute. It is calculated using the cardiac output formula: Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR). Stroke volume is the blood ejected by the heart with each contraction, and heart rate is the number of beats per minute. For example, if the stroke volume is 70 mL and the heart rate is 72 bpm, the cardiac output is 5040 mL/min or 5.04 L/min. This reflects how much blood the cardiovascular system circulates per minute under resting conditions.

Measuring cardiac output can be done using various techniques. Invasive methods such as the pulmonary artery catheter can directly assess CO through thermodilution (ScienceDirect, n.d.). Non-invasive options include echocardiography and Doppler ultrasound. The Fick Principle measures cardiac output based on oxygen consumption and the difference between venous and arterial blood oxygen content.

Higher cardiac output is often seen during exercise or stress, influenced by the autonomic nervous system, which regulates heart rate and contractility. Cardiac output is closely tied to systematic vascular resistance, influencing blood pressure and overall perfusion. Understanding how to measure cardiac output is essential for evaluating cardiac performance and circulatory health.

What is a Cardiac Output Equation?

The Cardiac Output Equation is a standardized clinical formula used to determine how much blood the heart pumps per minute. It is expressed as Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR). In practice, this equation allows healthcare professionals to quantify cardiac function by calculating cardiac output in liters per minute (L/min). The Carepatron Cardiac Output Equation template provides a structured format for inputting patient-specific values such as stroke volume and heart rate to generate accurate cardiac output results.

This tool supports clinicians in assessing cardiovascular performance, especially when diagnosing or managing cardiac-related conditions. By using this equation, professionals can interpret how effectively the heart circulates blood, aiding in the early detection of dysfunction and supporting treatment planning. The template also includes fields for documentation and clinical notes, ensuring that findings are recorded clearly and consistently for ongoing care and decision-making.

How does it work?

Carepatron’s Cardiac Output Equation template streamlines assessing cardiac function during patient evaluations. It guides medical professionals through structured steps to ensure accurate calculations, proper documentation, and informed decision-making—all within one easy-to-use platform.

Step 1: Access the template

Click the “Use template” button to immediately launch the Cardiac Output Equation template within the Carepatron platform. If you're not already set up, this action will direct you to download the Carepatron app, giving you instant access to the tool and other clinical resources.

Step 2: Use the template in patient assessment

Begin by filling out the patient information fields, including name, date of birth, gender, and current date. This ensures that all recorded cardiac output measurements are properly documented and associated with the correct patient for future clinical reference and reporting.

Step 3: Conduct the test by using the equation

Using available clinical data, input the patient’s heart rate (HR) and stroke volume (SV) into the equation field. The template will calculate the cardiac output (CO) automatically, providing a quick and reliable result that supports real-time decision-making during the evaluation.

Step 4: Discuss findings with patient

Review the results of the cardiac output calculation and interpret the findings in the context of the patient’s overall cardiovascular health. Use this opportunity to explain potential concerns, clinical implications, or the need for additional testing if abnormal values are observed.

Step 5: Provide patient support and next steps

Document any additional notes, recommendations, or follow-up plans directly in the template. Use the results to support treatment decisions, provide guidance on lifestyle or medication adjustments, and schedule further evaluation if cardiac output values suggest compromised function.

Results and interpretation

Interpreting cardiac output results requires a clinical understanding of how the heart’s ability to pump blood interacts with other hemodynamic parameters. A normal range for cardiac output is typically 5–6 L/min at rest in healthy adults (Young, 2010), but this varies depending on body size and physical condition. Low cardiac output (less than 4 L/min) may signal heart failure, shock, or aortic stenosis, while high cardiac output (over 8 L/min) may indicate severe anemia, sepsis, or increased oxygen delivery demands.

For accurate interpretation, cardiac output should be analyzed alongside systemic vascular resistance, arterial pressure, and cardiac index, which normalizes cardiac output to body surface area. Clinicians should also assess oxygen saturation, heart rate, and use the equation to calculate stroke volume when needed. Understanding the rate and stroke volume interplay provides deeper insight into central nervous system compensation or dysfunction. While the most accurate measurement method may vary by case, consistent interpretation of cardiac output results helps guide clinical decisions, optimize treatment plans, and monitor heart muscles under different physiological stresses.

Benefits of using this template

Using the Cardiac Output Equation template offers clear workflow advantages for healthcare professionals involved in cardiovascular assessment and monitoring. It provides a standardized method for calculating how effectively the heart pumps blood through the body, helping clinicians quickly identify deviations in cardiac performance. This is especially useful in managing critically ill patients, where precise, real-time data can influence treatment decisions. The template supports heart health evaluation by allowing professionals to observe changes in output related to heartbeats, arterial compliance, and the body's need to circulate red blood cells and oxygen to vital organs.

Simplifying documentation enhances efficiency during patient assessments and improves communication within care teams. It also supports monitoring in cases of heart disease, where reduced output may signal poor perfusion despite more blood vessels or normal body temperature. This structure ensures that the clinical significance of cardiac output findings is not missed, enabling better-informed interventions.

References

King, J., & Lowery, D. R. (2023, July 17). Physiology, cardiac output. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK470455/

ScienceDirect. (2018). Heart stroke volume – An overview. https://www.sciencedirect.com/topics/nursing-and-health-professions/heart-stroke-volume

ScienceDirect. (n.d.). Thermodilution – An overview. https://www.sciencedirect.com/topics/medicine-and-dentistry/thermodilution

Young, D. B. (2010). Control of cardiac output. Morgan & Claypool Life Sciences. https://www.ncbi.nlm.nih.gov/books/NBK54473/