Diastolic Murmurs Begin with S2 and Terminate Before S1
Diastolic murmurs characteristically begin with the onset of the S2 heart sound and terminate with or before the S1 heart sound. This is the fundamental timing characteristic that defines all diastolic murmurs, distinguishing them from systolic murmurs which occur between S1 and S2.
Timing and Physiologic Basis
The ACC/AHA guidelines clearly establish that diastolic murmurs occur during ventricular diastole, which begins when the semilunar valves close (S2) and ends when the atrioventricular valves close (S1) 1, 2.
Early diastolic murmurs begin with or shortly after S2, when ventricular pressure drops below aortic or pulmonary artery pressure. Classic examples include:
- High-pitched aortic regurgitation murmurs (decrescendo pattern)
- Pulmonic regurgitation with pulmonary hypertension
- These start immediately as the pressure gradient develops after valve closure 1
Middiastolic murmurs occur during early ventricular filling and typically originate from the mitral or tricuspid valves. They represent flow across stenotic or relatively narrowed valves during passive filling 1.
Presystolic murmurs occur during the period following atrial contraction (late diastole), just before S1, and require sinus rhythm. These are characteristic of mitral or tricuspid stenosis 1.
Why the Other Options Are Incorrect
S3 accompaniment: Diastolic murmurs are NOT always accompanied by an S3. While an S3 may be present in certain conditions (like severe mitral regurgitation causing increased diastolic flow), it is not a defining characteristic of diastolic murmurs 1.
Functional/innocent murmurs: Most innocent murmurs in children and young adults are midsystolic, not diastolic, originating from aortic or pulmonic outflow tracts. Innocent mid-diastolic murmurs are extremely rare (0.27% in one large study) 1, 3. Diastolic murmurs are typically pathologic and warrant investigation.
S1 to S2 timing: This describes systolic murmurs, not diastolic murmurs. Systolic murmurs begin after S1 (when ventricular pressure rises to open semilunar valves) and end before or at S2 1, 2.
Clinical Pitfalls
The presence of any diastolic murmur should prompt echocardiographic evaluation, as these are rarely innocent. The 2014 AHA/ACC guidelines emphasize that even subtle diastolic findings (like the opening snap in mitral stenosis) require careful assessment 4. Don't dismiss a diastolic murmur as benign without imaging confirmation.