A heart murmur is an extra sound heard through a stethoscope during a heartbeat, caused by turbulent blood flow through or near the heart valves. In adults, most murmurs are harmless and discovered incidentally during a routine exam. Some, however, signal underlying valve disease or other cardiac conditions that need attention. The distinction between an innocent murmur and a problematic one depends on when in the heartbeat it occurs, how it sounds, and whether it comes with other symptoms.
What Creates the Sound
Blood normally flows smoothly through your heart’s four chambers and valves. A murmur happens when that flow becomes rough or choppy, producing a whooshing or swishing noise. Think of it like water running through a garden hose versus water hitting a kink or a narrowed section: the disruption creates sound. This turbulence can result from blood moving faster than usual, flowing through a valve that’s too narrow or doesn’t close properly, or simply from a higher volume of blood passing through a normal heart.
Innocent vs. Abnormal Murmurs
Innocent murmurs (also called physiological or flow murmurs) are produced by normal blood flow through a structurally healthy heart. They’re extremely common in children but also occur in adults. These murmurs tend to be soft, change with body position, and disappear or fade when you hold your breath and bear down. No clicks or extra heart sounds accompany them.
Abnormal murmurs are created by a structural problem: a damaged valve, a hole between heart chambers, or thickened heart muscle. The timing of the murmur during the heartbeat is one of the strongest clues. A murmur that occurs as the heart squeezes blood out (a systolic murmur) is more likely to be innocent. A murmur heard while the heart fills with blood (a diastolic murmur) or one that runs continuously through the entire heartbeat almost always points to a real problem.
Common Causes in Adults
Valve Problems
The most frequent cause of an abnormal murmur in adults is valve disease. Two patterns account for the majority of cases. In stenosis, a valve becomes stiff or narrowed, forcing blood through a smaller opening. In regurgitation, a valve doesn’t close completely, allowing blood to leak backward. Aortic stenosis and mitral regurgitation are the two valve conditions doctors encounter most often in adult patients.
Mitral valve prolapse is a particularly common culprit. The flaps of the valve between the left upper and lower chambers bulge backward when the heart squeezes, preventing a tight seal. This allows blood to leak in the wrong direction. Risk factors for valve problems in general include aging, a history of heart attack, infections that affect the heart (such as endocarditis), rheumatic fever from untreated strep throat, radiation to the chest, and heart defects present since birth.
Some congenital heart defects aren’t caught until adulthood. A hole between the upper chambers of the heart (atrial septal defect) accounts for roughly one third of congenital defects first detected in adults. Its murmur can sound nearly identical to a common innocent childhood murmur, which is why it often goes unnoticed for decades.
Non-Cardiac Causes
Not every murmur comes from the heart itself. Conditions that increase the speed or volume of blood flow can create turbulence through perfectly normal valves. Anemia reduces the oxygen-carrying capacity of your blood, so your heart compensates by pumping faster and harder. An overactive thyroid gland does something similar by revving up your metabolism and heart rate. Pregnancy increases blood volume by about 50%, which can produce a flow murmur that disappears after delivery. Fever and severe dehydration can have the same effect temporarily.
Symptoms to Watch For
Many murmurs cause no symptoms at all. You could have one for years without knowing it. When a murmur does reflect an underlying problem, the symptoms come from that problem rather than from the murmur itself.
Signs that suggest something more serious include shortness of breath (especially with exertion or when lying flat), chest pain or tightness, heart palpitations, fainting or unusual weakness, a persistent cough, and swelling in your ankles or feet. Bluish discoloration of the skin is a less common but more urgent sign, indicating that your blood isn’t carrying enough oxygen. If a murmur is found alongside any of these symptoms, further testing is typically warranted right away.
Hypertrophic cardiomyopathy, a condition where the heart muscle becomes abnormally thick, deserves special mention. It produces a murmur that changes noticeably with position and exertion and can cause fainting, chest pain, and fatigue. It’s one of the more serious conditions that a murmur can reveal.
How Murmurs Are Evaluated
When a doctor hears a murmur, the first step is characterizing it right there with the stethoscope. They’ll note several features: where on the chest it’s loudest, when during the heartbeat it occurs, its pitch (high, medium, or low), and whether it changes when you shift position or exercise. Murmurs are graded on a scale from 1 to 6, with 1 being barely audible and 6 being so loud it can be heard without even pressing the stethoscope firmly to the chest.
The grade alone doesn’t determine severity. A grade 2 murmur from a significantly narrowed valve can be more dangerous than a louder innocent flow murmur. Context matters: the timing, the pitch, the presence of extra heart sounds, and your symptoms all factor in.
If there’s any suspicion the murmur is abnormal, the next step is an echocardiogram. This is the primary diagnostic tool. It uses ultrasound to create a moving picture of your heart, showing the valves opening and closing, the chambers contracting, and the direction of blood flow in real time. It can reveal a leaky valve, a narrowed opening, a hole between chambers, or thickened heart muscle. The test is painless, takes 30 to 60 minutes, and requires no special preparation.
What Happens After Diagnosis
If your murmur is innocent, no treatment is needed. You won’t have any restrictions on physical activity, and the murmur itself poses no health risk. Your doctor may not even mention it again at future visits.
If the murmur is linked to a valve problem, the next steps depend on how severe it is. Mild valve leaks or narrowing often require nothing more than periodic monitoring with repeat echocardiograms every year or two. You’ll likely feel fine and continue normal activities. Moderate to severe valve disease may need medication to manage symptoms like fluid retention or high blood pressure, reduce the heart’s workload, or prevent blood clots.
When valve disease becomes severe enough to strain the heart or limit daily life, valve repair or replacement becomes an option. Modern approaches range from open-heart surgery to catheter-based procedures where a new valve is delivered through a blood vessel in the leg, avoiding a large incision entirely. Recovery from catheter-based procedures is typically a few days, compared to several weeks for open surgery.
If the murmur is caused by a non-cardiac condition like anemia or an overactive thyroid, treating that underlying condition resolves the murmur. Once your blood counts normalize or your thyroid is brought under control, the extra heart sound disappears on its own.