A heart murmur is a sound, not a disease, but the conditions that produce certain murmurs can absolutely leave you drained. When a murmur signals an underlying valve problem or structural defect, the heart’s ability to pump blood efficiently drops, and the resulting shortfall in oxygen and nutrient delivery to your tissues shows up as fatigue. The connection between the whooshing sound your doctor hears and the exhaustion you feel runs through several overlapping mechanisms, and the specifics depend on which heart problem is generating the murmur in the first place.
Not All Murmurs Are Created Equal
A murmur is the audible result of turbulent blood flow inside the heart or great vessels. Research measuring sound energy inside arteries has confirmed a direct relationship between the intensity of turbulence and the loudness of the murmur a doctor hears at the chest wall.1PubMed. Turbulent blood flow in humans: its primary role in the production of ejection murmurs But turbulence can happen in a perfectly healthy heart, especially when blood is flowing quickly through normal structures. These are called innocent murmurs, and they are short, soft, and not associated with any cardiac disease. They are always systolic, meaning they occur while the heart is contracting, and they tend to be more noticeable when you are lying down.2Progress in Pediatric Cardiology. Evaluation of heart murmurs in children An innocent murmur will not cause fatigue or any other symptom. It is background noise from a heart that works fine.
The murmurs that matter are pathological ones, produced when something structural has gone wrong: a valve that does not open fully, a valve that leaks, a hole between chambers, or an abnormal connection between vessels. These conditions force the heart to work harder to maintain adequate blood flow, and over time the compensatory effort can fall short. That gap between what your body needs and what your heart can deliver is where fatigue begins.
How a Struggling Heart Starves Your Muscles
Your skeletal muscles are among the most demanding tissues in your body when it comes to blood supply, especially during physical activity. When a valve problem reduces the heart’s output, less blood reaches those muscles per minute. The consequence is measurable. Direct testing of muscle fatigue in people with chronic heart failure has shown that activating a large muscle like the quadriceps triggers rapid fatigue, and the likely cause is the cardiovascular system’s inability to supply enough blood flow for the work being asked of it.3PubMed Central. Direct measurement of skeletal muscle fatigue in patients with chronic heart failure
The problem goes deeper than simple blood volume, though. Reduced cardiac output sets off a cascade of changes in the muscles themselves. Chronically underperfused muscles shift their metabolism, become less efficient at extracting and using oxygen, and develop structural changes that make them fatigue faster even at low effort levels. Research into the mechanisms of skeletal muscle fatigability in heart failure points to reduced muscle perfusion and altered muscle metabolism as major contributing factors, likely triggered by a combination of low cardiac output and elevated sympathetic nervous system activity.4Frontiers in Physiology. Skeletal Muscle Fatigability in Heart Failure So the fatigue you feel is not just your heart struggling in the moment. Your muscles have been remodeled by weeks, months, or years of inadequate supply, and they tire out faster than they should even when resting cardiac output seems adequate.
Valve Conditions That Commonly Cause Fatigue
Different valve problems create fatigue through somewhat different routes, though they converge on the same outcome of reduced delivery to the body’s tissues.
Aortic stenosis, where the aortic valve narrows and restricts blood leaving the heart, is a classic culprit. People with aortic stenosis frequently develop exercise intolerance well before they experience dramatic symptoms like chest pain or fainting. Interestingly, the severity of the valve narrowing itself is not always the main driver. Research comparing patients with moderate versus severe aortic stenosis found that peak aerobic capacity did not significantly differ between the two groups. Instead, the patients who had the worst exercise tolerance were those whose heart muscle had developed dysfunction beyond the valve problem, including impaired squeezing of the left ventricle, stiffening of the heart during filling, and elevated pressures in the lung circulation.5European Heart Journal – Cardiovascular Imaging. Cardiac dysfunction rather than aortic valve stenosis severity drives exercise intolerance and adverse haemodynamics A broader study of patients with aortic stenosis who were classified as asymptomatic or minimally symptomatic found that effort intolerance was significantly linked to decreased function of the left ventricle, left atrium, and right ventricle.6PubMed Central. Prevalence, Mechanisms, and Prognostic Impact of Effort Intolerance in Patients With Asymptomatic/Minimally Symptomatic Aortic Stenosis The takeaway: with aortic stenosis, fatigue often reflects the downstream damage to the heart muscle, not just the tightness of the valve.
Mitral regurgitation, where the mitral valve leaks and allows blood to flow backward into the left atrium during contraction, creates fatigue through a slightly different path. Part of each heartbeat’s output goes the wrong direction, meaning less blood makes it out to the body. At the same time, the backward flow increases pressure in the lung veins, producing breathlessness alongside the fatigue. The combination of low cardiac output and pulmonary congestion explains why fatigue and shortness of breath are the dominant symptoms of chronic mitral regurgitation.7Current Problems in Cardiology. Mitral valve regurgitation
Congenital Defects and Oxygen Levels
Not every murmur-causing condition involves a valve. Congenital heart defects, such as holes between the heart’s chambers, can also produce murmurs and fatigue, but the mechanism sometimes involves oxygen levels directly. When blood shunts from the right side of the heart to the left through a defect between the atria, oxygen-poor blood bypasses the lungs and mixes with oxygen-rich blood heading out to the body. During exercise, when the body’s oxygen demand rises sharply, this shunting gets worse. In patients with right-to-left shunts through interatrial defects, oxygen saturation dropped from about 94% at rest to about 84% during exercise. After the defect was closed, resting oxygen saturation jumped to nearly 99%, and exercise capacity increased significantly, from roughly 7 metabolic equivalents to about 9.8PubMed. Right to left shunt through interatrial septal defects in patients with congenital heart disease: results of interventional closure That kind of oxygen desaturation during exertion produces the sort of heavy, whole-body fatigue that makes ordinary activities feel disproportionately hard.
Adults with congenital heart disease also show evidence of neurohormonal activation, even when they feel well. Compared to healthy individuals, they have substantially elevated levels of stress hormones and cardiac signaling molecules. These elevations climb in a stepwise fashion with worsening functional class, and the process begins before symptoms become obvious.9PubMed. Neurohormonal activation and the chronic heart failure syndrome in adults with congenital heart disease The chronic activation of the sympathetic nervous system and the renin-angiotensin system contributes to fluid retention, blood vessel constriction, and a general state of physiological stress that compounds the fatigue caused by reduced blood flow or oxygenation.
Anemia as a Double Hit
Sometimes the murmur and the fatigue share a single non-cardiac root cause. Severe anemia is a perfect example. When your hemoglobin drops low enough, the heart compensates by pumping faster and harder to deliver enough oxygen with fewer red blood cells. That hyperdynamic circulation produces a flow murmur, the kind a doctor hears and might initially flag. At the same time, your tissues are oxygen-starved at the cellular level, making you profoundly tired.
If anemia becomes chronic and severe, the compensatory workload can push the heart into what is called high-output heart failure. The lower blood viscosity and increased vasodilation triggered by anemia reduce the resistance the heart pumps against, which sounds like it would be helpful but actually forces the heart to move more volume with each cycle. The neurohormonal activation and fluid retention that follow can tip the balance into frank heart failure.10PubMed Central. Chronic anemia complicated by cardiac failure, pulmonary hypertension, and pericardial effusion: a case report In this scenario, treating the anemia itself, rather than the murmur or the heart, is what resolves both the sound and the exhaustion.
General Fatigue Versus Exertional Fatigue
If you have a heart condition and feel tired, it is worth paying attention to when the fatigue hits. Researchers studying fatigue in heart failure have argued that general fatigue and exertional fatigue are two meaningfully different phenomena. General fatigue is a pervasive sense of low energy that persists even at rest, and it can overlap with depression, poor sleep, medication side effects, and deconditioning. Exertional fatigue, by contrast, is the inability to sustain physical effort. When breathlessness accompanies exertional fatigue, it may point specifically to a low-output state or more advanced heart failure, which would call for a different clinical response than general tiredness.11PubMed Central. Fatigue in Persons with Heart Failure: A Systematic Literature Review and Meta-Synthesis Using the Biopsychosocial Model of Health
This distinction matters practically. If your fatigue is mainly exertional and comes with shortness of breath, your doctor may want to investigate whether your valve disease has progressed or whether your heart’s pumping function has worsened. If the fatigue is more generalized, other contributors like anemia, thyroid problems, sleep disruption, or medication effects may deserve attention alongside the cardiac workup.
How Medications Factor In
Heart conditions that produce murmurs are often treated with medications that can themselves affect energy levels. Observational studies of people with heart failure have found that beta-blockers, which slow the heart rate and reduce the force of contraction, were associated with decreased exertional fatigue but did not appear to affect general fatigue. Diuretics and nitrates, on the other hand, were associated with increased fatigue of both kinds. Psychotropic medications showed a particularly strong link: people taking them at baseline were more than five times as likely to follow a severe exertional fatigue trajectory.11PubMed Central. Fatigue in Persons with Heart Failure: A Systematic Literature Review and Meta-Synthesis Using the Biopsychosocial Model of Health
This creates a tricky balancing act. Beta-blockers are essential in many forms of heart failure because they reduce the heart’s workload and improve long-term survival, and the evidence suggests they may actually help with effort-related tiredness. But diuretics, which are critical for managing fluid overload, can cause fatigue through dehydration and electrolyte shifts. If you feel worse after a medication change, that conversation with your cardiologist is worth having rather than just assuming the heart condition itself has worsened.
When Reduced Blood Flow Reaches the Brain
Fatigue is not purely a muscular phenomenon. Chronic reductions in cardiac output also affect the brain. Cognitive symptoms like difficulty concentrating, mental fog, and forgetfulness are common complaints among people with heart failure and structural heart disease, and they sometimes get lumped under the general umbrella of “fatigue” when a more precise description would be mental exhaustion.
The mechanism involves sustained low perfusion of the brain over time. Research has identified a strong association between cardiovascular conditions, including heart failure, low cardiac index, and valvular disease, and reduced cerebral blood flow. In older adults whose brain perfusion is already diminished by age, additional reductions in blood supply from cardiac problems appear to increase the risk of cognitive decline.12PubMed Central. Cardiovascular risk factors promote brain hypoperfusion leading to cognitive decline and dementia This means the “brain fog” some people with heart murmur-causing conditions describe is not imagined or simply a byproduct of poor sleep. It has a physiological basis in reduced cerebral perfusion.
Sleep Disruption as a Hidden Amplifier
Heart conditions associated with murmurs often coexist with sleep-disordered breathing, which worsens fatigue independently. Obstructive sleep apnea is common in people with various forms of structural heart disease. In the specific case of patients who have undergone Fontan palliation for complex congenital heart disease, sleep apnea is particularly concerning because the altered circulation lacks a pumping chamber for the lung circulation. Any increase in airway resistance during sleep raises pulmonary vascular resistance and reduces cardiac output further.13Cambridge University Press. Non-invasive management of obstructive sleep apnoea in a Fontan patient
Even in less complex heart conditions, undiagnosed sleep apnea can be the hidden factor turning moderate fatigue into something debilitating. Repeated oxygen desaturations overnight prevent restorative sleep and elevate sympathetic nervous system activity around the clock. If you have a known murmur-causing heart condition and your fatigue seems out of proportion to your cardiac status, a sleep evaluation may uncover an addressable problem.
What Happens to Fatigue After Treatment
For many valve conditions, surgical repair or replacement is the definitive treatment. The expectation is that fixing the valve will restore normal blood flow and resolve the fatigue, and that often happens, but the recovery is rarely instant or straightforward.
After mitral valve replacement for ischemic mitral regurgitation, one study found that patients who received mechanical valves improved their six-minute walking distance from about 242 meters before surgery to about 290 meters afterward. Patients receiving biological valves, however, did not show a statistically significant improvement.14PubMed. Exercise Hemodynamic and Functional Capacity After Mitral Valve Replacement in Patients With Ischemic Mitral Regurgitation: A Comparison of Mechanical Versus Biological Prostheses On the aortic side, the trajectory can also be unexpected. Men who underwent aortic valve replacement for chronic aortic regurgitation showed a roughly 12% decline in peak exercise capacity over a four-year follow-up, corresponding to an annual decrease of about 2-3%.15PubMed Central. Decreased aerobic capacity 4 years after aortic valve replacement in male patients operated upon for chronic aortic regurgitation This does not mean surgery failed; it may reflect the heart muscle changes that accumulated before surgery, the effects of aging, or inadequate rehabilitation afterward.
The lived experience of recovery tracks with these numbers. Qualitative research on patients after heart valve replacement found that people universally struggled with weakness and a changed body in the months following surgery. The process of regaining physical strength and reestablishing a sense of normalcy was long, though most eventually reported returning to their daily lives with renewed vitality.16PubMed Central. Patient experiences of recovery after heart valve replacement: suffering weakness, struggling to resume normality If you or someone you know is heading into valve surgery expecting the fatigue to vanish on the operating table, recalibrating those expectations may help. Recovery is real, but it takes months, and structured cardiac rehabilitation plays a meaningful role in how much exercise capacity ultimately comes back.
Why “Just a Murmur” Deserves Follow-Up
One of the most common misconceptions about heart murmurs is that the label itself tells you everything you need to know. Plenty of people are told they have a murmur during a routine exam, and the murmur turns out to be entirely innocent. But a murmur accompanied by fatigue, breathlessness, or reduced exercise tolerance warrants more investigation. Echocardiography, which uses ultrasound to visualize the heart’s structure and function in real time, is the standard tool for distinguishing an innocent murmur from one produced by a valve problem or structural defect.
Even conditions that produce no murmur at all can contribute to fatigue through cardiac mechanisms. Research on chronic fatigue syndrome identified a subset of patients with unusually small hearts and reduced cardiac output on echocardiography, with smaller left ventricular dimensions and lower stroke volumes than healthy controls.17PubMed Central. Small heart syndrome in patients with chronic fatigue syndrome These patients’ cardiac function fluctuated alongside their symptom flares and remissions, with the heart performing worse during periods of increased fatigue.18Journal of Cardiology. Cardiac function fluctuates during exacerbation and remission in young adults with chronic fatigue syndrome and “small heart” The relationship between cardiac output and fatigue, in other words, extends well beyond classical valve disease. If persistent fatigue is your main complaint, a thorough cardiac evaluation can be revealing even when no obvious murmur is present.