Cardiac Output Calculator

Cardiac output (CO) is the volume of blood the heart pumps per minute. It equals heart rate (HR) multiplied by stroke volume (SV): CO = HR x SV. At rest, a healthy adult has a cardiac output of approximately 4.0 to 8.0 liters per minute. During intense exercise, cardiac output can reach 20 to 25 L/min in trained athletes.

The Fick equation estimates cardiac output from oxygen consumption and the arteriovenous oxygen difference: CO = VO2 / (CaO2 - CvO2), where VO2 is oxygen consumption in mL/min, CaO2 is arterial oxygen content, and CvO2 is venous oxygen content (both in mL O2 per 100 mL blood). The simpler formula CO = HR x SV is derived from basic cardiac physiology and is the most commonly used clinical calculation.

Normal resting cardiac output for adults is 4.0 to 8.0 L/min. Cardiac index (CI), which adjusts for body surface area, is typically 2.5 to 4.0 L/min/m2. A low cardiac output (below 4.0 L/min) may indicate heart failure, hypovolemia, or cardiogenic shock. A high cardiac output may occur in sepsis, fever, or hyperthyroidism.

Stroke volume (SV) is the volume of blood ejected per heartbeat, typically 60 to 100 mL in a resting adult. Cardiac output equals heart rate multiplied by stroke volume. An athlete with a resting heart rate of 50 bpm and a stroke volume of 100 mL has a cardiac output of 5.0 L/min, which is similar to an untrained person at 75 bpm and 67 mL SV.

Cardiac output is affected by heart rate, stroke volume, preload (venous return to the heart), afterload (resistance the heart pumps against), and contractility (force of cardiac muscle contraction). These are summarized by the Frank-Starling mechanism: increased preload leads to increased stroke volume and therefore increased cardiac output, up to physiological limits.