Which equation represents cardiac output?

• A. CO = Heart Rate x Stroke Volume
• B. CO = Blood Pressure x Heart Rate
• C. CO = Cardiac Index x Systemic Vascular Resistance
• D. CO = MAP - Right Atrial Pressure

Answer: (A)

The main idea is that how much blood the heart pumps each minute (cardiac output) comes from how fast the heart beats and how much blood is moved with each beat. That makes the equation CO = HR × SV the correct representation. Heart rate is measured in beats per minute and stroke volume in milliliters per beat, so multiplying them gives milliliters per minute, the volume pumped each minute. For example, a heart rate of 70 beats per minute with a stroke volume of 70 mL per beat yields about 4,900 mL/min (roughly 4.9 L/min), which fits typical resting values.

The other expressions mix different physiological quantities that don’t directly yield flow. Blood pressure is a force, not a volume flow; multiplying it by heart rate doesn’t give cardiac output. The relationship involving mean arterial pressure and systemic vascular resistance is CO ≈ MAP / SVR (a ratio, not a product), and using a product like cardiac index times systemic vascular resistance doesn’t align dimensionally with cardiac output. MAP minus right atrial pressure is a pressure gradient, not a flow measure.