During cardiac auscultation, a systolic murmur is heard. Which is the most common site of origin of a systolic murmur in a healthy young adult with no structural heart disease?

Explanation

## Innocent (Functional) Systolic Murmurs in Healthy Young Adults **Key Point:** Pulmonary flow murmurs are the most common innocent systolic murmurs in healthy young adults, arising from increased blood flow across a structurally normal pulmonary valve. ### Classification of Systolic Murmurs | Murmur Type | Mechanism | Prevalence in Healthy Young | Pathological? | |-------------|-----------|---------------------------|---------------| | Pulmonary flow | Increased RV stroke volume | Most common innocent | No | | Aortic flow | Increased LV stroke volume | Common innocent | No | | Vibratory/Still's | Vibration of chordae tendinae | Common in children | No | | Mitral regurgitation | Valve insufficiency | Pathological | Yes | | Aortic stenosis | Valve narrowing | Pathological | Yes | | Tricuspid regurgitation | Valve insufficiency | Pathological | Yes | ### Characteristics of Pulmonary Flow Murmur 1. **Location:** Left infraclavicular area, 2nd–3rd intercostal space 2. **Timing:** Early to mid-systolic, does NOT extend to A~2~ 3. **Quality:** Soft, low-pitched, vibratory 4. **Increases with:** Inspiration (increased venous return to RV), fever, anemia, pregnancy, hyperthyroidism 5. **Associated findings:** Normal S~2~, no clicks, no diastolic murmur **High-Yield:** Innocent murmurs are distinguished from pathological murmurs by the **absence of associated cardiac findings** — no thrills, no heaves, normal pulse character, normal JVP, and normal echocardiography. **Clinical Pearl:** The pulmonary flow murmur is particularly common in tall, thin young adults and athletes due to increased stroke volume and a more vertical heart position. It disappears with Valsalva maneuver (decreased preload) and increases with leg raise (increased preload). **Mnemonic:** **INNOCENT** = **I**nspiration increases it, **N**o associated findings, **N**ormal S~2~, **O**ccurs in young healthy, **C**an disappear with Valsalva, **E**arly systolic, **N**o diastolic component, **T**ransient with hemodynamic changes.