Cardiac Flow and Murmurs: One Diagram That Answers Most Questions

Murmur questions look like memorisation and are not. Nearly all of them can be reconstructed from two things: the path blood takes through the heart, and which valves are open in which phase. Get those solid and you can derive the answer instead of recalling it.

The circuit, in order

Say it out loud until it needs no effort:

Superior and inferior vena cava → right atrium → tricuspid valve → right ventricle → pulmonic valve → pulmonary artery → lungs → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta → body

Two facts fall out of it that get tested directly. The pulmonary artery carries deoxygenated blood and the pulmonary veins carry oxygenated blood — the only place in the body where the naming runs against the usual rule. And the left ventricle generates systemic pressure, which is why it hypertrophies under pressure loads and why left-sided lesions dominate adult cardiology.

Phases and what is open

Now the logic. A murmur is turbulent flow. In systole, turbulence can only come from blood forcing through a narrowed semilunar valve (stenosis) or leaking backwards through an incompetent AV valve (regurgitation). In diastole, it is the mirror image: a narrowed AV valve or a leaking semilunar valve. Every classic murmur is one of those four combinations.

Auscultation sites

Use the diaphragm for high-pitched sounds — most murmurs, S1, S2 — and the bell, held lightly, for low-pitched ones: S3, S4 and the rumble of mitral stenosis.

The murmurs worth knowing cold

Aortic stenosis

Systolic crescendo–decrescendo murmur at the right upper sternal border, radiating to the carotids. Often with a slow-rising, low-volume pulse and an S4. The classic symptom triad is angina, syncope and dyspnoea; the appearance of symptoms is prognostically important.

Mitral regurgitation

Holosystolic blowing murmur at the apex, radiating to the axilla. Often with an S3 in significant regurgitation.

Mitral stenosis

An opening snap after S2 followed by a low-pitched diastolic rumble at the apex — best heard with the bell, patient in the left lateral decubitus position. Associated with prior rheumatic fever and with atrial fibrillation as the atrium dilates.

Aortic regurgitation

Early diastolic decrescendo murmur at the left sternal border, best heard sitting forward at end expiration. Look for a widened pulse pressure and bounding peripheral pulses.

Tricuspid regurgitation

Holosystolic murmur at the left lower sternal border that increases with inspiration. Look for elevated jugular venous pressure and peripheral oedema.

Mitral valve prolapse

Mid-systolic click, sometimes followed by a late systolic murmur, at the apex. The manoeuvre response is the diagnostic feature: standing or Valsalva makes the click occur earlier and the murmur longer.

Hypertrophic cardiomyopathy

Harsh systolic murmur at the left lower sternal border that increases with Valsalva and on standing and decreases with squatting or handgrip. This is the inverse of almost every other murmur, and it is the reason the manoeuvre table below is worth memorising. Classic stem: a young athlete with exertional syncope or a family history of sudden cardiac death.

Ventricular septal defect

Harsh holosystolic murmur at the left lower sternal border. Counterintuitively, smaller defects tend to produce louder murmurs.

Manoeuvres: the highest-yield table in cardiology

Two shortcuts: right-sided murmurs love inspiration, and HOCM and MVP behave backwards compared with everything else.

Innocent versus pathologic

A common paediatric item. Features favouring an innocent murmur:

• Systolic only, never diastolic
• Soft — grade 1 or 2, no thrill
• No radiation
• Musical or vibratory in quality (the Still murmur, at the left lower sternal border)
• Changes with position, typically quieter on standing or sitting up
• Normal S2 with normal splitting
• Asymptomatic child with normal growth, normal pulses and no cyanosis

Features demanding evaluation:

• Any diastolic murmur. There is no innocent diastolic murmur.
• Grade 3 or louder, or any thrill
• Holosystolic timing
• Radiation, particularly to the back or neck
• Abnormal or absent femoral pulses (think coarctation)
• Symptoms: poor feeding, failure to thrive, exercise intolerance, cyanosis, syncope
• A family history of sudden cardiac death or congenital heart disease

Extra sounds

• S3 — early diastole, just after S2. Volume overload and a rapidly filling ventricle. Can be normal in children, young adults and pregnancy; in an older adult with dyspnoea it suggests heart failure.
• S4 — late diastole, just before S1. Atrial contraction into a stiff ventricle: hypertension, aortic stenosis, ischaemia, hypertrophy. Absent in atrial fibrillation, because there is no organised atrial contraction to produce it.

A four-step method for any murmur item

1. Timing. Systolic or diastolic? Diastolic narrows the field immediately and is never innocent.
2. Location and radiation. Carotids suggests aortic stenosis; the axilla suggests mitral regurgitation.
3. Manoeuvre response, if the stem gives one. Louder on Valsalva points hard at HOCM or MVP.
4. The rest of the stem. A young athlete with syncope, an older adult with angina and syncope, a child with absent femoral pulses — the surrounding detail usually confirms what the murmur suggested.