# Heart Murmurs USMLE: Sound to Diagnosis

> How do you match a murmur to a diagnosis on USMLE?

A three-step method for murmur vignettes, with a full valve lesion table and the preload-afterload logic behind every bedside maneuver.

Time the murmur first: systolic murmurs are AS, MR, MVP, HOCM, VSD and tricuspid regurgitation, while diastolic murmurs are AR and MS and are always pathologic. Then use location and radiation to pick the valve, and confirm with a maneuver that changes preload or afterload. Louder with Valsalva means HOCM or MVP.

## How do you match a murmur to a diagnosis on USMLE?

**Decision one is timing.** Systole opens the widest list; diastole narrows you to aortic regurgitation or mitral stenosis; a murmur running continuously through S2 is a patent ductus arteriosus until proven otherwise. Timing alone eliminates most choices.

**Decision two is location plus radiation.** The murmur is loudest over the structure receiving the turbulent jet and radiates along it: AS from the right second intercostal space to the carotids, MR from the apex to the axilla. HOCM sits at the left lower sternal border and radiates nowhere -- the most useful discriminator against aortic stenosis.

Maneuvers are the tiebreaker, not the starting point: reach for them when timing and location leave two lesions standing, classically HOCM versus AS. The same preload-afterload logic runs through [Cardiology](/topics/cardiology), and the tracing in the stem often carries the other half of the answer, so pair this with [how to read an ECG on the USMLE](/blog/how-to-read-ecg-usmle).

## The master murmur reference table

| Lesion | Timing | Loudest at | Radiation | Maneuver effect | Classic patient |
| --- | --- | --- | --- | --- | --- |
| **Aortic stenosis (AS)** | Crescendo-decrescendo systolic | Right 2nd ICS | Carotids | ↓ Valsalva/standing; ↓ handgrip | Elderly, syncope, pulsus parvus et tardus |
| **Aortic regurgitation (AR)** | Early decrescendo diastolic | Left 3rd-4th ICS, sitting forward | Toward apex | ↑ handgrip; ↑ squatting | Wide pulse pressure, water-hammer pulse, Marfan |
| **Mitral stenosis (MS)** | Opening snap, mid-diastolic rumble | Apex, lateral decubitus | Minimal | ↑ squatting/leg raise | Rheumatic disease, pregnancy, atrial fibrillation |
| **Mitral regurgitation (MR)** | Holosystolic, blowing | Apex | Axilla | ↑ handgrip/squatting; ↓ Valsalva | Post-MI papillary muscle rupture |
| **Mitral valve prolapse (MVP)** | Mid-systolic click, late systolic murmur | Apex | Axilla if regurgitant | ↑ Valsalva/standing; ↓ squatting | Young woman, Marfan or Ehlers-Danlos |
| **HOCM** | Crescendo-decrescendo systolic | Left lower sternal border | None | ↑ Valsalva/standing; ↓ squatting/handgrip | Young athlete, exertional syncope, family sudden death |
| **Ventricular septal defect (VSD)** | Harsh holosystolic | Left lower sternal border | Across precordium | ↑ handgrip; ↓ Valsalva | Infant failing to thrive; days 3-5 post-MI |
| **Patent ductus arteriosus (PDA)** | Continuous, machine-like | Left infraclavicular | Left back | ↑ handgrip | Congenital rubella, preterm neonate |
| **Tricuspid regurgitation (TR)** | Holosystolic | Left lower sternal border | Right sternal border | ↑ inspiration (Carvallo) | Injection drug use endocarditis; pulmonary HTN |
| **Atrial septal defect (ASD)** | Systolic flow murmur, **wide fixed split S2** | Left 2nd ICS | Minimal | Split fixed through respiration | Young adult, paradoxical embolic stroke |

## What each maneuver does to preload and afterload

Murmur intensity tracks the volume of blood crossing the lesion -- except in HOCM and MVP, where a smaller ventricle worsens obstruction or prolapse. Learn the hemodynamic change, not a list.

| Maneuver | Preload | Afterload | Louder | Softer |
| --- | --- | --- | --- | --- |
| Valsalva (strain) | ↓ | ↓ | HOCM, MVP | AS, MR, AR, VSD |
| Standing from squat | ↓ | ↓ | HOCM, MVP | AS, MR, AR, VSD |
| Squatting | ↑ | ↑ | AS, MR, AR, MS, VSD | HOCM, MVP |
| Passive leg raise | ↑ | No change | AS, MR, MS | HOCM, MVP |
| Sustained handgrip | ↑ slightly | ↑↑ | MR, AR, VSD, PDA | AS, HOCM |
| Inspiration | ↑ right-sided | No change | TR and other right-sided murmurs | Left-sided murmurs |

**Passive leg raise is the clean experiment**, since squatting raises preload and afterload at once while leg raise changes preload alone. **Handgrip is the pure afterload test:** higher vascular resistance pushes more blood backward through an incompetent mitral or aortic valve and across a VSD, while the outflow gradient in AS and HOCM falls.

## High-yield murmur associations

**The mid-systolic click is pathognomonic for mitral valve prolapse.** With Valsalva or standing the ventricle shrinks, the leaflet prolapses earlier, and the click moves toward S1; squatting delays it.

**A systolic murmur that gets louder with Valsalva in a young athlete is HOCM,** because less preload means a smaller cavity and worse dynamic outflow obstruction.

**Aortic stenosis in an older adult presents with syncope, angina and dyspnea.** The carotid upstroke is delayed and weak -- pulsus parvus et tardus; severe disease gives a late-peaking murmur with a soft A2. A bicuspid valve explains the lesion at fifty.

**A continuous machine-like murmur under the left clavicle is a PDA**, because aorta-to-pulmonary-artery flow never stops at S2. Indomethacin closes the duct; prostaglandin E1 holds it open for duct-dependent lesions.

Chronic MR and AR dilate the ventricle and present as heart failure, where [HFrEF vs HFpEF](/blog/hfref-vs-hfpef-usmle) drives management.

## The 10-second murmur ID decision tree

> **Exam-day cheat sheet.** 1) Diastolic = AR or MS; continuous = PDA. 2) Apex radiating to axilla = MR; add a click = MVP. 3) Right upper sternal border to carotids = AS. 4) Left lower sternal border, no radiation = HOCM if louder with Valsalva, VSD if harsh holosystolic, TR if louder with inspiration. 5) Fixed split S2 = ASD.

## How murmurs are tested in vignettes

**A 17-year-old collapses at basketball practice; a left lower sternal border systolic murmur increases on standing.** Answer HOCM, with asymmetric septal hypertrophy and systolic anterior motion of the mitral valve.

**A 74-year-old has exertional chest pain, syncope and delayed carotid upstrokes.** Answer severe aortic stenosis; valve replacement, not medical therapy, is the intervention.

**A patient three days after an inferior MI develops a new apical holosystolic murmur with pulmonary edema.** Answer papillary muscle rupture causing acute MR; a young adult with cryptogenic stroke and a fixed split S2 is instead an ASD with paradoxical embolism.

## Common wrong-answer traps

**Trap: calling a left lower sternal border systolic murmur aortic stenosis.** AS radiates to the carotids and softens with Valsalva; HOCM does neither.

**Trap: treating the ASD murmur as the defect itself.** The sound is flow across the pulmonic valve; the diagnostic finding is the wide fixed split S2.

**Trap: assuming handgrip lowers preload like Valsalva.** Handgrip raises afterload, making regurgitant murmurs louder and outflow murmurs softer.

**Trap: dismissing a diastolic murmur as functional.** Systolic flow murmurs can be benign; diastolic and continuous murmurs are pathologic and need echocardiography.

## Sources

- [ACC/AHA valvular heart disease guidelines](https://www.acc.org/Guidelines)
- [USMLE Step 1 content outline](https://www.usmle.org/step-exams/step-1)

Murmur questions reward pattern recognition under time pressure, built only by repetition against real stems. [Practice valvular disease questions on StepGenie](https://dashboard.stepgenie.app/sign-up) and drill maneuvers until timing, location and Valsalva response arrive together.

## Frequently asked questions

### How do you tell aortic stenosis from HOCM?

Aortic stenosis and HOCM both produce crescendo-decrescendo systolic murmurs, but AS is loudest at the right second intercostal space and radiates to the carotids, while HOCM sits at the left lower sternal border and radiates nowhere. Valsalva and standing drop preload and make HOCM louder while softening AS; squatting and passive leg raise reverse that. Sustained handgrip softens both, so it cannot separate them.

### Which murmurs get louder with Valsalva?

Only two commonly tested murmurs get louder during the strain phase of Valsalva: hypertrophic obstructive cardiomyopathy and mitral valve prolapse. Reduced venous return shrinks the left ventricle, which worsens dynamic outflow obstruction in HOCM and lets the mitral leaflet prolapse earlier, moving the click toward S1. Every other murmur, including aortic stenosis and mitral regurgitation, becomes softer because less blood crosses the lesion.

### What does sustained handgrip do to a murmur?

Sustained handgrip raises systemic vascular resistance, so it increases afterload rather than preload. More blood is driven backward across an incompetent valve, making mitral regurgitation, aortic regurgitation, VSD and PDA murmurs louder. The same rise in afterload lowers the gradient across the left ventricular outflow tract, so aortic stenosis and HOCM murmurs get softer. Handgrip also delays the mitral valve prolapse click.

### Which murmurs are always pathologic?

Diastolic and continuous murmurs are always pathologic and require echocardiography. A diastolic murmur means aortic or pulmonic regurgitation, or mitral or tricuspid stenosis; a continuous machine-like murmur points to a patent ductus arteriosus. Systolic murmurs can be benign flow murmurs, particularly soft early systolic murmurs in children, pregnancy or anemia, but a holosystolic or late-peaking systolic murmur is not benign.

### Why is the split S2 fixed in an atrial septal defect?

In an atrial septal defect, continuous left-to-right shunting keeps right ventricular volume elevated throughout the respiratory cycle, so pulmonic valve closure stays delayed whether the patient inhales or exhales, giving a wide and fixed split S2. The audible murmur is a systolic ejection murmur from increased flow across the pulmonic valve, not turbulence through the defect itself.

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Canonical page: [Heart Murmurs USMLE: Sound to Diagnosis](https://www.stepgenie.app/blog/valvular-heart-disease-murmur-usmle)
Topic hub: [Cardiology](https://www.stepgenie.app/topics/cardiology)