What Causes a Child's Heart Murmur to Become Quieter at Follow-Up
A child's heart murmur becomes quieter at follow-up most commonly because it was an innocent murmur that naturally varies with physiologic conditions, particularly positional changes, or because the child has grown and hemodynamic conditions have changed. 1
Innocent Murmurs That Characteristically Become Quieter
The most common innocent murmurs in children have specific patterns of becoming quieter or disappearing with certain maneuvers or positions:
- Still's murmur disappears or becomes quieter and localizes to the left lower sternal border when the child assumes an upright position 1
- Innocent pulmonary systolic murmur disappears with upright positioning 1
- Venous hum disappears completely with jugular venous compression or when the child lies supine 1
- Carotid bruit disappears with bilateral shoulder hyperextension 1
- Physiologic pulmonary artery stenosis does not disappear with maneuvers but is only heard in infants under 6 months of age, so it naturally resolves as the infant grows 1
Pathologic Murmurs That May Become Quieter
While less common, certain pathologic conditions can result in quieter murmurs at follow-up:
- Small ventricular septal defects (VSDs) may become quieter or disappear as they spontaneously close over time, which occurs in many cases during the first years of life 2
- Patent ductus arteriosus may close spontaneously in neonates, resulting in disappearance of the murmur 1
- Improved cardiac function after treatment of conditions like myocarditis or cardiomyopathy may result in decreased turbulent flow and a quieter murmur 1
Critical Distinction: When a Quieter Murmur Is Reassuring vs. Concerning
A murmur becoming quieter is generally reassuring if:
- The child remains asymptomatic with normal growth and development 3
- The murmur demonstrates classic innocent murmur characteristics (positional variation, appropriate quality and location) 1
- Physical examination otherwise remains normal with good peripheral perfusion and normal S2 3
However, a quieter murmur warrants immediate concern if:
- The child develops new symptoms such as decreased exercise tolerance, syncope, chest pain, or signs of heart failure 4, 3
- The murmur becomes quieter in the context of worsening ventricular function, as decreased cardiac output can paradoxically reduce murmur intensity 1
- There are new abnormal physical findings such as abnormal S2, gallop rhythm, or signs of poor perfusion 3
Clinical Approach to the Quieter Murmur
When evaluating a child whose murmur has become quieter:
- Repeat the examination in multiple positions (supine, sitting, standing) to determine if the murmur demonstrates innocent characteristics 1
- Assess for any new symptoms including exercise intolerance, syncope, chest pain, or feeding difficulties in infants 4, 3
- Verify normal growth parameters and age-appropriate exercise capacity 3
- If the original murmur was pathologic or possibly pathologic, echocardiography is indicated to assess for spontaneous closure of defects or changes in hemodynamics 1, 2
- If the murmur was clinically diagnosed as innocent and remains consistent with innocent characteristics, no further testing is needed 2, 3
Common Pitfall to Avoid
Do not assume that a quieter murmur always indicates improvement. In the setting of deteriorating cardiac function (such as severe aortic stenosis progressing to heart failure), decreased cardiac output can actually make a previously loud murmur become softer, which represents clinical deterioration rather than improvement. 4 Always correlate the change in murmur intensity with the overall clinical picture, symptoms, and functional status.