What Is a Heart Murmur? What It Means and When to Worry.

A heart murmur is a sound heard through a stethoscope that represents turbulent blood flow within or near the heart. The presence of a murmur is a physical examination finding, not a diagnosis. What it means depends entirely on its cause, and the cause determines whether it requires treatment, monitoring, or nothing at all.

The Mechanism

Blood normally flows through the heart in organized, laminar streams. When flow becomes turbulent, either because it is moving too fast, passing through a narrowed opening, or moving backward through a valve that is not closing properly, it generates audible vibrations. Those vibrations are the murmur. A stethoscope placed on the chest picks up the sound, and an experienced clinician can characterize its timing (systolic or diastolic), intensity, location, radiation pattern, and quality. Each of these features narrows the differential.

The timing is the most important first cut. Systolic murmurs occur when the ventricles contract and push blood forward. They are far more common and include most innocent murmurs, as well as clinically significant causes like aortic stenosis and mitral regurgitation. Diastolic murmurs occur when the ventricles fill. Diastolic murmurs are almost always pathological and should always be investigated with echocardiography. A continuous murmur that persists through both systole and diastole is rarer and suggests patent ductus arteriosus or arteriovenous fistula.

The intensity of a murmur is graded on a scale of 1 to 6. Grade 1 is barely audible; grade 4 and above is associated with a palpable thrill, a vibration felt with the hand on the chest wall. Intensity correlates imperfectly with severity. A very soft murmur can represent severe disease if the underlying valve gradient has dropped because the ventricle is failing. This is one reason stethoscope findings alone are never sufficient to grade valvular severity.

What the Evidence Shows

The foundational guidance document for murmur evaluation is the 2014 AHA/ACC valvular heart disease guideline (Nishimura et al., Journal of the American College of Cardiology, 2014), updated in 2021. It provides the evidence framework for echocardiographic thresholds, intervention timing, and follow-up intervals across all valve lesions. 4 / Promising

Functional murmurs. Functional (or flow) murmurs arise when blood flows more rapidly through structurally normal valves. This occurs in states of increased cardiac output: fever, anemia, hyperthyroidism, pregnancy, and vigorous exercise. They are typically soft, systolic, and best heard at the left sternal border. They resolve when the underlying condition resolves and carry no independent cardiovascular risk. The 2014 AHA/ACC guideline does not recommend echocardiographic evaluation when the clinical context makes a functional murmur the clear diagnosis.

Aortic stenosis. The most common valvular heart disease requiring intervention in adults over 65. Population studies, including the Cardiovascular Health Study (Otto et al., New England Journal of Medicine, 2000), found aortic valve sclerosis (thickening without obstruction) in 26 percent of adults over 65, with progression to frank stenosis in approximately 2 percent per year. Once a patient develops severe aortic stenosis, the median survival without intervention is 2 to 3 years from the onset of symptoms, with a risk of sudden death that increases sharply after symptom onset. The clinical sound is a harsh, crescendo-decrescendo systolic murmur loudest at the right upper sternal border, often radiating to the carotids.

Aortic regurgitation. A high-pitched diastolic decrescendo murmur audible at the left sternal border, best heard with the patient leaning forward. The Henry Ford Heart and Vascular Institute longitudinal data and pooled series reviewed by Maurer and colleagues (Journal of the American College of Cardiology, 2019) document that chronic severe aortic regurgitation is associated with annual rates of left ventricular decompensation of approximately 4 to 6 percent per year even in asymptomatic patients, which is why serial echocardiographic monitoring is required at defined intervals.

Mitral regurgitation. A holosystolic murmur at the apex radiating to the axilla. The Framingham Heart Study data show mitral regurgitation is present in approximately 10 percent of the general population, with most cases mild. The clinical significance depends on mechanism and severity. The MIDAS registry and data from the Mitral Regurgitation International Database (MIDA) investigators demonstrate that in severe primary mitral regurgitation, surgical repair before the development of symptoms or left ventricular dysfunction (ejection fraction below 60 percent or end-systolic dimension above 40 mm) produces meaningfully better outcomes than waiting for symptoms.

Mitral valve prolapse. Produces a mid-systolic click, sometimes followed by a late systolic murmur. The Framingham data estimate a prevalence of approximately 2 to 3 percent in the general population. Most cases are benign; the subset with severe mitral regurgitation from flail leaflet or significant prolapse requires surgical evaluation. A study by Avierinos and colleagues (Circulation, 2002) followed 833 patients with mitral valve prolapse and found a 10-year cardiac event rate substantially higher in those with significant regurgitation than in those without, reinforcing the need for echocardiographic characterization to separate the benign majority from the higher-risk minority.

The Echocardiogram’s Role

The stethoscope identifies that a murmur is present. The echocardiogram tells the physician what is causing it, how severe it is, and what it has done to the heart over time. A transthoracic echocardiogram visualizes the valve leaflets and their motion, uses Doppler techniques to quantify the pressure gradient across the valve and the volume of any regurgitant flow, and assesses the downstream consequences: left ventricular size and function, left atrial size, pulmonary artery pressure. These measurements determine the grade of disease severity, which in turn determines the intervention threshold and follow-up interval.

A murmur that has never been evaluated with echocardiography is incompletely characterized. A murmur that was evaluated with echocardiography years ago may have progressed. The timing of follow-up echocardiography depends on the valve lesion and severity class; the 2021 AHA/ACC guideline provides specific intervals for each.

When echocardiography is technically limited by body habitus or lung interference, a transesophageal echocardiogram (TEE) can be performed. A probe is passed into the esophagus, which lies immediately posterior to the heart, and provides high-resolution images of the valves and cardiac structures that are not possible from the chest wall. TEE is particularly useful for evaluating the mitral valve anatomy before surgical planning, for identifying vegetations in suspected endocarditis, and for precisely characterizing the mechanism of mitral regurgitation.

Cardiac MRI is a third imaging modality increasingly used in valvular assessment. It provides highly accurate quantification of regurgitant volumes and fractions for aortic and mitral regurgitation, and is used when echocardiographic measurements are discordant or uncertain. Its primary limitation is availability and cost.

Intervention Timing: When the Valve Needs Treatment

The decision to repair or replace a valve is based on a combination of symptom status, imaging-based severity markers, and ventricular function. The fundamental principle in valvular heart disease is that intervention is most effective when performed before irreversible ventricular damage occurs, but after the evidence for benefit is clear enough to justify procedural risk.

For aortic stenosis, the Class I indication for aortic valve replacement is the development of symptoms, specifically syncope, angina, or heart failure, in a patient with severe stenosis. The 2021 AHA/ACC guideline also supports intervention in asymptomatic severe stenosis when left ventricular ejection fraction falls below 50 percent, or when the patient is undergoing other cardiac surgery. Transcatheter aortic valve replacement (TAVR) has expanded options significantly: the PARTNER 3 trial (Mack and colleagues, New England Journal of Medicine, 2019) demonstrated that TAVR was non-inferior to surgical replacement in low-risk patients, with lower rates of stroke, death, or rehospitalization at 1 year. TAVR is now standard of care in most patients with severe symptomatic aortic stenosis, depending on anatomy.

For mitral regurgitation from a degenerative (prolapse or flail leaflet) cause, surgical repair is strongly preferred over replacement when anatomy is suitable because repair preserves the subvalvular apparatus and produces better long-term left ventricular function. The CTSN trial data and observational series from high-volume centers show 10-year freedom from reoperation above 90 percent for successful repair of degenerative mitral regurgitation. Experienced centers perform mitral valve repair with low operative mortality, making early referral to a center with this expertise appropriate for men with severe primary mitral regurgitation.

Endocarditis: The Infection Risk That Changes Dental Care

Infective endocarditis (IE) is a bacterial infection of the heart valve surfaces. Patients with structurally abnormal valves, from any cause including aortic stenosis, mitral valve prolapse with significant regurgitation, bicuspid aortic valve, rheumatic mitral disease, or prior valve repair or replacement, are at elevated risk because abnormal valve surfaces create the turbulence and surface irregularity that allows circulating bacteria to adhere and colonize. The connection between valvular disease and dental care is specific and evidence-based, not merely precautionary.

The mechanism: bacteremia, a transient shower of bacteria into the bloodstream, occurs routinely during dental procedures including tooth extraction, scaling, and root planing. In most people, bacteremia is brief and cleared by normal immune defenses. In patients with abnormal valves, the bacteremia creates an opportunity for bacteria, most commonly Streptococcus viridans from the oral cavity and Staphylococcus aureus from skin or medical procedures, to colonize the roughened valve surface and form a vegetation: a mass of bacteria, fibrin, and platelets that grows on the valve.

Vegetation growth causes valvular dysfunction, destroys valve architecture, and serves as a reservoir for septic embolism, fragments that break off and lodge in the brain (causing stroke), kidneys, spleen, or other organs. IE carries an in-hospital mortality of approximately 15-20 percent in most registries and long-term morbidity from valve destruction requiring surgical intervention.

The 2007 AHA guideline change. The approach to endocarditis prophylaxis was significantly revised by the American Heart Association in 2007 (Wilson et al., Circulation). The previous approach recommended prophylaxis broadly for a wide range of valvular conditions. The revised guideline substantially narrowed indications, limiting prophylactic antibiotics before dental procedures to the highest-risk conditions: prosthetic valves, prior IE, specific congenital heart defects (cyanotic CHD, repaired CHD with prosthetic material, cardiac transplant recipients with valvulopathy). The revision was based on evidence that spontaneous bacteremia from normal daily activities (chewing, tooth brushing) is far more frequent than procedure-related bacteremia, making intermittent prophylaxis of uncertain net benefit against background risk. 4 / Promising

The implication for most patients with native valve disease: prophylaxis is not indicated for routine dental care. Maintaining excellent oral hygiene, reducing the bacterial burden in the mouth that reaches the bloodstream even with normal activities, is a more meaningful ongoing intervention than intermittent antibiotic prophylaxis before dental visits.

Exceptions that do require prophylaxis. Patients with prosthetic valves (mechanical or biological), patients who have had a previous episode of infective endocarditis, or patients who have had certain congenital heart repairs involving prosthetic material should receive prophylaxis before procedures that produce significant gingival bleeding. The standard regimen is amoxicillin 2g orally 30 to 60 minutes before the procedure, or clindamycin 600mg for penicillin-allergic patients. Patients in these categories should carry a card or note in their medical records identifying their prophylaxis status, and they should inform every dental provider.

For patients with murmurs and valvular disease generally. Know specifically whether your valve condition qualifies for endocarditis prophylaxis under the 2007 AHA guidelines, not whether you have “a heart condition.” The generic instruction “tell your dentist you have a heart problem” is clinically insufficient. The specific question to ask your cardiologist is: “Does my specific valvular condition require antibiotic prophylaxis before dental procedures?” The answer changes management and may change the answer your dentist receives.

What to Do This Week

1. Confirm whether an echocardiogram has been performed. If a clinician has told you that you have a heart murmur, ask directly whether an echocardiogram was obtained. If not, ask why, and whether one is indicated. The stethoscope finding alone does not characterize the murmur’s cause or severity.

2. Check how old your last echocardiogram is. If you had an echocardiogram for a murmur more than 3 years ago and do not know your follow-up schedule, confirm that schedule with your physician. Valvular disease progresses, and the follow-up interval is clinically determined by the lesion type and severity grade.

3. Report any new symptoms promptly. New exertional breathlessness, chest pressure with exertion, near-fainting with activity, or episodes of rapid pounding heartbeat in a person with known valvular disease change the clinical urgency. These are not symptoms to defer to the next scheduled appointment. Contact your physician or cardiologist promptly.

4. Understand your lesion and its grade. Ask your physician or cardiologist to explain which valve is affected, whether the problem is stenosis (narrowing) or regurgitation (leaking), and what the severity grade is. These are the variables that determine your follow-up interval and eventual intervention threshold.

5. If you have a diastolic murmur and no echocardiogram, request one. Diastolic murmurs are rarely innocent in adults. If a diastolic murmur has been noted on examination and no imaging has been performed, that gap should be closed.

A murmur identified in an adult is not something to file away and forget. It is a physical finding that deserves proper characterization, a severity grade, and a documented follow-up plan. Most will prove clinically unimportant. The ones that are not will be significantly better managed for having been properly evaluated at the outset.

The Signal Check is fifteen questions mapping the cardiovascular risk pattern across the physiological domains most commonly missed in standard screenings. It produces a specific starting point for your next clinical conversation.