Systolic vs Diastolic Murmurs: A Timing-First Framework

A murmur classification guide for USMLE and clinical practice · Updated 2026

Every murmur question gets easier once you answer one thing first: when does it happen? Systole is the gap between S1 ("lub") and S2 ("dub"); diastole is the longer gap after S2 before the next S1. Time the murmur against a palpated carotid pulse — the pulse coincides with systole — and you've already halved your differential.

Systolic murmurs (between S1 and S2)

These are common and often benign. The high-yield causes:

• Aortic stenosis — harsh crescendo-decrescendo at the right upper sternal border, radiates to the carotids.
• Mitral regurgitation — blowing holosystolic murmur at the apex, radiates to the axilla.
• Tricuspid regurgitation — holosystolic at the lower left sternal border, louder on inspiration.
• Hypertrophic cardiomyopathy — louder with standing/Valsalva (less filling).
• Innocent flow murmur — soft, early, no radiation; common in young, healthy hearts.

Diastolic murmurs (after S2)

These are almost always pathologic — take them seriously.

• Aortic regurgitation — high-pitched, blowing, early-diastolic decrescendo at the left sternal border; heard best sitting forward in expiration.
• Mitral stenosis — low-pitched, rumbling, mid-to-late diastolic at the apex, often with an opening snap; use the bell.

Then refine with shape, pitch and maneuvers

Once timing is fixed, layer on the details: crescendo-decrescendo vs holosystolic, high vs low pitch, and dynamic maneuvers (inspiration accentuates right-sided murmurs; standing and Valsalva reduce most murmurs except HCM and mitral valve prolapse). These are the tie-breakers between murmurs that share a timing.