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🫀 Heart Murmurs — A Clear, Detailed Guide

What Is a Heart Murmur?

Your heart makes two normal sounds — "lub" (S1) and "dub" (S2) — as its valves snap shut with each beat. A heart murmur is an extra whooshing, swishing, or rumbling sound heard between those two normal sounds. It is caused by turbulent blood flow — similar to the sound of water rushing through a narrow garden hose.

Murmurs are not diseases themselves; they are sounds that may (or may not) indicate an underlying problem.

Why Does Turbulence Happen?

Three main mechanisms create turbulence:

Mechanism	Example
Blood forced through a narrowed opening	Aortic stenosis (stiff aortic valve)
Blood leaking backward through a faulty valve	Mitral regurgitation
Blood flowing through an abnormal hole	Ventricular septal defect (VSD)
Increased speed of normal flow	Fever, pregnancy, anemia

Innocent vs. Pathological Murmurs

✅ Innocent (Benign) Murmurs

Also called functional murmurs — the heart is structurally normal, but blood is moving faster than usual.

Causes: fever, pregnancy, anemia, hyperthyroidism, exercise, childhood growth spurts.

Features that suggest a murmur is innocent:

Soft (grade 1–2/6)
Mid-systolic (heard in the middle of the heartbeat)
No other symptoms
No radiation to the neck or axilla
Normal ECG and chest X-ray

These murmurs require no treatment and often disappear on their own.

⚠️ Pathological (Abnormal) Murmurs

Caused by a structural problem in the heart. Red flags include:

Loud murmur (grade ≥ 3/6) or harsh quality
Diastolic murmur (diastolic murmurs are almost always pathological)
Holosystolic (pan-systolic) — lasts the entire heartbeat
Associated symptoms: chest pain, breathlessness, fainting, cyanosis (bluish lips)
Abnormal ECG or chest X-ray

Timing — The Most Important Feature

The cardiac cycle has two phases:

Systole = ventricles contract, blood is pumped out
Diastole = ventricles relax, filling with blood

Murmurs are classified by when they occur:

1. Systolic Murmurs

Heard during the heartbeat (between lub and dub).

Type	When it occurs	Classic Cause
Mid-systolic (ejection)	Peaks in mid-systole; crescendo-decrescendo shape	Aortic stenosis, pulmonic stenosis
Holosystolic (pansystolic)	Entire systole, same intensity throughout	Mitral regurgitation, tricuspid regurgitation, VSD
Late systolic	Starts mid-systole and continues to S2	Mitral valve prolapse

2. Diastolic Murmurs

Heard between heartbeats (between dub and next lub). Always pathological.

Type	Classic Cause
Early diastolic (high-pitched, blowing, decrescendo)	Aortic regurgitation, pulmonary regurgitation
Mid-diastolic (low rumble)	Mitral stenosis, tricuspid stenosis
Presystolic (crescendo just before S1)	Mitral stenosis (in sinus rhythm)

3. Continuous Murmurs

Start in systole and continue through S2 into diastole — never stops. Classic cause: Patent Ductus Arteriosus (PDA) — described as a "machinery murmur."

Grading — How Loud Is It?

Murmurs are graded on a scale of 1 to 6:

Grade	Description
1/6	Very faint — barely audible, only in a quiet room
2/6	Soft but clearly heard
3/6	Moderate, no thrill (vibration on chest wall)
4/6	Loud + thrill present
5/6	Very loud, heard with stethoscope barely on chest
6/6	Heard without a stethoscope

Grades 1–2 are usually innocent. Grades ≥3 warrant further investigation.

Key Murmurs You Should Know

Aortic Stenosis (AS)

Type: Mid-systolic ejection murmur
Sound: Harsh, crescendo-decrescendo
Location: Right upper sternal border (2nd intercostal space)
Radiates to: Neck (carotid arteries)
Cause: Stiffened/calcified aortic valve; blood can't flow out easily
Associated: Weak, slow-rising carotid pulse ("pulsus parvus et tardus")

Mitral Regurgitation (MR)

Type: Holosystolic (pansystolic)
Sound: Blowing, uniform intensity throughout systole
Location: Apex (left side of chest)
Radiates to: Axilla (armpit)
Cause: Leaky mitral valve; blood jets backward into left atrium

Mitral Stenosis (MS)

Type: Mid-diastolic rumble
Sound: Low-pitched, rumbling, follows an "opening snap"
Location: Apex, best heard with the bell of the stethoscope with the patient in left lateral decubitus
Cause: Narrowed mitral valve (often from rheumatic fever); blood can't flow from left atrium to left ventricle

Aortic Regurgitation (AR)

Type: Early diastolic
Sound: High-pitched, blowing, decrescendo
Location: Left sternal border, 3rd/4th intercostal space
Cause: Leaky aortic valve; blood leaks back from aorta into left ventricle during diastole

Mitral Valve Prolapse (MVP)

Type: Mid-to-late systolic murmur preceded by a click
Trick: Standing/Valsalva → click moves earlier, murmur lengthens; squatting → click moves later, murmur shortens

Patent Ductus Arteriosus (PDA)

Type: Continuous "machinery" murmur
Location: Left upper sternal border/infraclavicular area
Cause: A fetal blood vessel (ductus arteriosus) fails to close after birth

Murmur Patterns at a Glance

Diagram of principal heart murmurs A-H showing timing relative to S1 and S2

Harrison's Principles of Internal Medicine — Murmur patterns: A=presystolic, B=holosystolic, C=aortic ejection, D=pulmonic ejection, E=early diastolic, F=mid-diastolic (mitral stenosis), G=short mid-diastolic, H=continuous (PDA)

Bedside Maneuvers That Change Murmur Intensity

These tricks help doctors identify the cause:

Maneuver	Effect on blood volume	What increases
Valsalva (bearing down)	↓ venous return	HOCM, MVP
Standing	↓ preload	HOCM, MVP
Squatting	↑ preload & afterload	AS, MR, AR (most others louder)
Inspiration	↑ right-sided flow	Right-sided murmurs (tricuspid, pulmonic)
Expiration	↑ left-sided flow	Left-sided murmurs (mitral, aortic)

When to Get Further Tests

Flowchart for evaluating cardiac murmurs

The key decision points:

Soft systolic murmur + no symptoms + normal ECG/CXR → No further workup needed
Loud systolic (≥3/6), holosystolic, or diastolic/continuous → Echocardiogram (ultrasound of the heart)
Echocardiography confirms valve anatomy, measures pressure gradients, and quantifies regurgitation

Summary Table

Feature	Innocent	Pathological
Grade	1–2/6	≥3/6 (often)
Timing	Mid-systolic	Diastolic, holosystolic, or late systolic
Quality	Soft, musical	Harsh, blowing, rumbling
Symptoms	None	Dyspnea, chest pain, syncope
Treatment	None needed	Treat underlying cause

Sources: Harrison's Principles of Internal Medicine, 22nd Ed. (2025); The Harriet Lane Handbook, 23rd Ed.

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