Cardiac Output Calculator

Cardiac Output equals Stroke Volume times Heart Rate

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What Is Cardiac Output?

Cardiac output (CO) measures the total volume of blood the heart pumps per minute. It reflects how effectively the heart delivers oxygenated blood to tissues and organs throughout the body. Clinicians routinely assess cardiac output to evaluate hemodynamic stability, guide fluid resuscitation, and titrate vasoactive medications in critical care settings.

Worked Example

A resting adult has a stroke volume of 70 mL and a heart rate of 72 beats per minute. Using the formula Q = SV × HR, the cardiac output is 70 × 72 = 5,040 mL/min, or 5.04 L/min. This falls within the normal range of 4–8 L/min, indicating adequate cardiac performance at rest.

The Formula Explained

The cardiac output equation multiplies stroke volume (SV) by heart rate (HR). Stroke volume is the amount of blood ejected from the left ventricle with each heartbeat, typically 60\u201380 mL in a healthy adult at rest. Heart rate is the number of contractions per minute. Their product yields cardiac output in mL/min, which is converted to L/min by dividing by 1000. For a resting adult with an SV of 70 mL and HR of 72 bpm, cardiac output equals 5.04 L/min.

Normal Ranges

A healthy adult at rest typically has a cardiac output between 4 and 8 L/min. During vigorous exercise, trained athletes can achieve outputs exceeding 20 L/min. Cardiac Index (CI) normalizes CO to body size by dividing by body surface area (BSA). Normal CI ranges from 2.5 to 4.0 L/min/m\u00B2. Values below 2.2 L/min/m\u00B2 may indicate cardiogenic shock, while elevated values can occur with sepsis, hyperthyroidism, or pregnancy.

Clinical Significance

Monitoring cardiac output helps clinicians differentiate among types of shock (cardiogenic, distributive, hypovolemic, and obstructive), optimize fluid management, and assess the effectiveness of inotropic therapies. Cardiac Index is particularly valuable because it accounts for patient size, making it a more reliable indicator when comparing across populations. In the ICU, serial CI measurements help guide treatment decisions and predict patient outcomes.

Frequently Asked Questions

What affects cardiac output?

Four primary factors determine cardiac output: preload (venous return), afterload (arterial resistance), contractility (myocardial force), and heart rate. Changes in any of these variables alter the volume of blood the heart delivers each minute.

How is cardiac output measured clinically?

The gold standard is thermodilution via a pulmonary artery catheter. Less invasive methods include echocardiography (Doppler-based measurements), arterial pulse contour analysis, and bioimpedance/bioreactance techniques. Each method has trade-offs in accuracy, invasiveness, and continuous monitoring capability.

Why use Cardiac Index instead of Cardiac Output?

A cardiac output of 4 L/min might be adequate for a small adult but insufficient for a large individual. By dividing CO by body surface area, the Cardiac Index provides a size-normalized value that enables more meaningful comparison across patients of different body sizes.

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