What would be the heart rate of a person if the cardiac output is 5 L, blood volume in the ventricles at the end of diastole is 100 mL and at the end of ventricular systole is 50 mL?

Cardiac Output

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NCERT Class 11 · Body Fluids and Circulation · 1 NEET question

A resting heart beats 72 times per minute, but your cardiac output remains constant at 5 litres. If your stroke volume drops, your heart rate must compensate to maintain systemic perfusion. Do not confuse stroke volume with cardiac output; one is a single beat, the other is a minute's work.

The idea

Cardiac output is the volume of blood pumped by each ventricle per minute. It is the mathematical product of stroke volume and heart rate. The formula is: Cardiac Output = Stroke Volume × Heart Rate. The average value is 5000 mL or 5 litres per minute in a healthy individual.

Why it matters

To meet the metabolic demands of the body tissues by ensuring adequate blood flow per unit of time.

NEET lens

NEET frequently tests the formula application. Expect numerical problems where you must calculate output given stroke volume and heart rate. Remember: the value is for 'each' ventricle, not the sum of both. Do not ignore the units; NCERT specifies 5000 mL, so watch for conversion traps in MCQ options.

Clinical significance

When cardiac output falls below the physiological requirement, the body enters cardiogenic shock. This failure leads to inadequate tissue oxygenation and multi-organ dysfunction. Chronic low output is a hallmark of congestive heart failure.

Introduction

Cardiac output (CO) is the volume of blood pumped by each ventricle per minute. CO = Stroke Volume (SV) × Heart Rate (HR). At rest: ~5 litres/minute. During exercise: can reach 20–25 litres/minute.

Core concept

Formula: CO = SV × HR. Normal resting values: HR = 72 bpm. SV = 70 mL/beat. CO = 72 × 70 = ~5040 mL/min ≈ 5 L/min. Stroke Volume (SV): volume ejected per beat. SV = End-Diastolic Volume (EDV) - End-Systolic Volume (ESV). EDV ~120-130 mL. ESV ~50-60 mL. SV ~70 mL. Ejection fraction (EF) = SV/EDV = 70/120 ≈ 58% (normal >55%). During exercise: HR increases + SV increases → CO up to 20-25 L/min.

Go deeper

Factors affecting CO: (1) Preload (venous return) — more filling → greater stretch → stronger contraction (Starling's law) → higher SV. (2) Afterload (aortic pressure) — higher BP → harder to eject → lower SV. (3) Contractility — sympathetic stimulation → stronger contraction → higher SV. (4) Heart rate — sympathetic stimulation → higher HR → higher CO (but very high HR → less filling time → lower SV → may reduce CO).

From Class 10

The heart pumps a certain volume of blood every minute. This is the cardiac output — how much blood the heart delivers to the body per minute.