Heart Murmurs in Dogs

A heart murmur is an abnormal sound detected during cardiac auscultation when a veterinarian listens to your dog's heart with a stethoscope. Rather than hearing only the normal rhythmic heart sounds produced by valve closure, the veterinarian hears an additional whooshing, swishing, or blowing sound caused by turbulent blood flow within the heart or great vessels. Heart murmurs are not diseases themselves but rather clinical findings that may indicate underlying cardiac abnormalities requiring further evaluation. The significance of a heart murmur ranges from completely benign findings requiring no treatment to indicators of serious heart disease requiring comprehensive management.

Heart murmurs are among the most common cardiovascular findings in dogs, detected in a significant percentage of canine veterinary examinations. The prevalence varies considerably by dog age, breed, and population studied. Innocent or physiologic murmurs are commonly heard in puppies, with many resolving by four to five months of age as the cardiovascular system matures. In adult dogs, heart murmurs become increasingly common with age as acquired heart diseases develop, with studies suggesting that by senior age, a substantial proportion of dogs in certain breeds have detectable murmurs. Small breed dogs show particularly high rates of murmurs associated with degenerative valve disease, while large breeds may develop murmurs from different underlying conditions.

The severity of heart murmurs is assessed through a grading system ranging from grade one, barely audible and detected only with careful listening, to grade six, so loud it can be felt as a vibration through the chest wall and heard even without direct stethoscope contact. However, murmur grade does not directly correlate with the severity of underlying heart disease in all cases. Some significant cardiac conditions produce soft murmurs, while some benign conditions or non-cardiac causes can produce loud murmurs. The character, timing, and location of the murmur, along with other clinical findings, help determine its significance and guide decisions about further evaluation and treatment needs.

Understanding heart murmurs matters to dog owners because this common finding often generates significant concern when reported, yet the clinical implications vary enormously from completely insignificant to requiring urgent treatment. Knowing that a murmur alone does not constitute a diagnosis helps owners engage productively in discussions with their veterinarian about whether further testing is warranted and what the findings might mean for their dog's health and longevity. Many dogs with murmurs live completely normal lives without any cardiac impact, while others require ongoing monitoring or treatment. The key lies in appropriate evaluation to distinguish between these scenarios.

This comprehensive guide will help you understand what heart murmurs are and what causes them, how veterinarians assess and grade murmurs, and what different murmur characteristics suggest about underlying cardiac status. You will learn about the various conditions that can cause heart murmurs in dogs, from innocent puppy murmurs to serious cardiac diseases. Understanding the diagnostic process, including when echocardiography is recommended and what it reveals, prepares you for informed decision-making about your dog's cardiac evaluation and care. Guidance about monitoring, treatment, and prognosis helps you know what to expect when living with a dog diagnosed with a heart murmur.

Heart murmurs result from turbulent blood flow that produces audible vibrations as blood moves through the heart and great vessels. Normal blood flow is laminar, moving smoothly in parallel layers, and produces minimal sound. When blood flow becomes turbulent due to increased velocity, changes in blood viscosity, or structural abnormalities that disrupt flow patterns, the resulting vibrations create the characteristic murmur sound. Understanding the mechanisms that produce turbulent flow helps explain why so many different conditions can cause heart murmurs and why the clinical significance varies so widely.

Innocent or physiologic murmurs occur in the absence of structural heart disease and represent one of the most common causes of murmurs in young dogs. These soft, grade one to two murmurs result from normal flow turbulence during the growth phase when the cardiovascular system is still maturing. Puppy murmurs are very common, particularly audible during periods of rapid growth or when heart rate is elevated. Most innocent puppy murmurs resolve by four to five months of age as the heart and vessels develop adult proportions. Excitement, fever, anemia, or other conditions that increase heart rate or blood flow velocity can also produce innocent murmurs in dogs of any age. These flow murmurs disappear when the inciting condition resolves.

Degenerative valve disease, also called myxomatous mitral valve disease or chronic valve disease, is the most common cause of pathologic heart murmurs in adult dogs, particularly small breed dogs. This condition involves progressive degeneration of the heart valves, most commonly the mitral valve separating the left atrium and left ventricle. As the valve thickens and distorts, it fails to close properly, allowing blood to leak backward during contraction. This regurgitant flow creates turbulence that produces a characteristic systolic murmur. The murmur typically intensifies gradually over time as valve degeneration progresses. Degenerative valve disease can eventually lead to heart enlargement and congestive heart failure, though many affected dogs never progress to clinical disease.

Congenital heart defects present from birth can cause murmurs detected in puppies that, unlike innocent murmurs, persist and may indicate significant structural abnormalities. Patent ductus arteriosus, an abnormal vessel connection that should close shortly after birth, produces a continuous machinery-like murmur. Subaortic stenosis, narrowing below the aortic valve, causes a systolic murmur often heard loudest at the heart base. Pulmonic stenosis, narrowing of the pulmonic valve, similarly produces a systolic murmur. Ventricular septal defects, holes between the ventricles, create murmurs from blood flow through the abnormal opening. Some congenital defects can be surgically corrected, while others require medical management or simply monitoring depending on severity.

Other conditions causing heart murmurs include dilated cardiomyopathy, where a weakened, enlarged heart may develop functional valve leakage creating murmurs. Endocarditis, infection of the heart valves, damages valve structures and causes turbulent flow. Anemia reduces blood viscosity and increases flow velocity, producing functional murmurs that resolve when anemia is corrected. Hyperthyroidism, though less common in dogs than cats, increases cardiac output and can create murmurs. Heartworm disease can cause murmurs through multiple mechanisms. Tumors affecting cardiac structures may disrupt normal flow patterns.

Risk factors for clinically significant heart murmurs parallel risk factors for underlying cardiac diseases. Small breed dogs face high risk for degenerative valve disease-related murmurs, with Cavalier King Charles Spaniels, Dachshunds, Chihuahuas, and similar breeds commonly affected. Large and giant breeds have higher rates of dilated cardiomyopathy-related murmurs. Certain breeds show predisposition to specific congenital defects. Age strongly influences murmur risk, with innocent murmurs common in puppies and acquired disease murmurs increasing with age. Family history of cardiac disease increases risk in predisposed breeds. Male dogs may have slightly higher risk for some conditions. Dogs without heartworm prevention in endemic areas risk developing murmurs from cardiac damage.

Heart murmurs themselves produce no symptoms that owners can detect at home because the abnormal sound is audible only through stethoscopic examination. Dogs with heart murmurs may be completely asymptomatic, with the murmur discovered incidentally during routine examination or pre-anesthetic evaluation. Early warning signs that might indicate progression to symptomatic heart disease include subtle changes in energy level that owners may initially attribute to normal aging, slightly reduced enthusiasm for walks or play, mild intermittent coughing that seems infrequent enough to dismiss, or minor changes in breathing patterns. Recognizing that these subtle changes in a dog known to have a heart murmur might indicate disease progression helps ensure timely reevaluation.

When heart murmurs are associated with progressive heart disease, symptoms develop that reflect the underlying cardiac dysfunction rather than the murmur itself. Coughing often becomes the first noticeable symptom, particularly occurring at night or in the early morning, triggered by heart enlargement pressing on the airways or fluid accumulation in the lungs. Exercise intolerance develops as the compromised heart cannot meet the body's demands during activity, causing dogs to tire more quickly, breathe harder during exertion, or refuse exercise they previously enjoyed. Breathing changes including increased respiratory rate and visible effort at rest indicate more advanced disease. These symptoms indicate that a murmur has progressed beyond an isolated finding to clinically significant heart disease.

Behavioral changes accompanying the transition from asymptomatic murmur to symptomatic heart disease reflect the impact of reduced cardiac function on overall wellbeing. Dogs may become less playful and more sedentary, preferring to rest rather than engage in usual activities. Appetite often decreases, and weight loss may occur. Sleep patterns may change, with restlessness at night caused by breathing difficulty when lying flat. Some dogs seem anxious or show signs of distress, possibly related to the sensation of breathlessness. Social withdrawal and reduced interaction with family members can occur as dogs feel progressively unwell. Noting these behavioral shifts in dogs with known murmurs helps identify emerging cardiac decompensation.

Physical signs associated with heart murmurs depend on whether underlying disease has progressed to cause hemodynamic changes. The murmur itself has characteristic features that provide diagnostic information: its timing relative to the cardiac cycle, its location on the chest where it is loudest, its radiation pattern, its pitch and quality, and its intensity grade. Dogs with compensated heart disease may show only the murmur without other physical abnormalities. Progressive disease produces heart enlargement detectable on examination, abnormal heart rhythms, increased respiratory rate, pale or bluish mucous membranes, weak pulses, jugular vein distension, or abdominal enlargement from fluid accumulation.

Progression from isolated murmur to symptomatic disease varies greatly depending on the underlying cause. Innocent puppy murmurs resolve without progression. Many dogs with degenerative valve disease maintain stable, low-grade murmurs for years without developing symptoms, and some never progress to clinical disease. Others show gradual intensification of murmurs paralleling disease progression, eventually developing congestive heart failure symptoms. Congenital defects vary widely in their natural history depending on the specific abnormality and its severity. Dogs with cardiomyopathy-related murmurs may progress rapidly or more slowly depending on the specific condition. Regular monitoring helps track any murmur changes and identify early signs of disease progression requiring intervention.

Veterinary examination and murmur detection begins with thorough cardiac auscultation using a stethoscope to listen to all valve areas of the heart. Your veterinarian will characterize any murmur detected according to its grade, timing within the cardiac cycle, point of maximal intensity, radiation pattern, and quality. They will note whether the rhythm is regular or irregular and assess overall heart rate. The rest of the physical examination evaluates for signs of cardiac disease or heart failure including respiratory changes, pulse quality, mucous membrane color, and evidence of fluid accumulation. The combination of murmur characteristics and physical examination findings guides decisions about further diagnostic workup.

Diagnostic testing recommendations depend on the murmur's characteristics and clinical context. Soft grade one or two murmurs in young puppies with no other abnormalities may warrant only monitoring, with recheck in several weeks to months to confirm resolution of presumed innocent murmurs. Persistent or louder murmurs, murmurs with characteristics suggesting specific abnormalities, or murmurs in breeds predisposed to cardiac disease warrant more thorough evaluation. Chest radiographs assess heart size and shape and evaluate for pulmonary changes suggesting heart failure. Electrocardiography detects rhythm abnormalities and some evidence of chamber enlargement. Echocardiography provides definitive diagnosis by visualizing heart structure, identifying specific abnormalities causing the murmur, and assessing cardiac function.

Echocardiography, or cardiac ultrasound, represents the gold standard for evaluating heart murmurs because it allows direct visualization of cardiac structures and blood flow. This non-invasive test shows chamber sizes, wall thickness, valve appearance and function, and abnormal structures if present. Doppler echocardiography visualizes blood flow patterns and can quantify the severity of valve leakage or stenosis. The information obtained from echocardiography often dramatically changes management compared to relying on murmur characteristics alone, as it may identify significant disease requiring treatment in dogs with soft murmurs or reveal benign findings in dogs with impressive-sounding murmurs. Referral to a veterinary cardiologist for echocardiography may be recommended for optimal evaluation.

Treatment for heart murmurs depends entirely on the underlying cause and whether associated cardiac disease requires intervention. Innocent murmurs in puppies require no treatment, only monitoring to confirm resolution. Dogs with degenerative valve disease and murmurs but no symptoms may need only monitoring, though evidence suggests early medication in some cases may slow disease progression. Once heart failure develops, medical management with diuretics, cardiac medications, and dietary modification becomes necessary. Certain congenital defects may be correctable through surgery or interventional procedures. Secondary murmurs from anemia or other conditions resolve with treatment of the underlying problem. The treatment approach is guided by the specific diagnosis rather than the murmur itself.

Monitoring and follow-up for dogs with heart murmurs varies based on the underlying diagnosis and disease stage. Dogs with stable murmurs and no evidence of significant disease may need only periodic rechecks, perhaps annually. Dogs with progressive conditions like degenerative valve disease benefit from more frequent monitoring, with echocardiographic reassessment periodically to track disease progression. Dogs receiving cardiac medications require regular rechecks to assess response and adjust treatment. Owners should monitor at home for any symptoms suggesting disease progression, particularly coughing, breathing changes, or exercise intolerance.

Cost considerations for heart murmur evaluation and management vary based on the extent of diagnostic workup needed. Basic examination and murmur detection is included in standard examination fees. Chest radiographs typically cost one hundred to three hundred dollars. Echocardiography ranges from three hundred to seven hundred dollars at general practices to somewhat more at specialty facilities or when performed by cardiologists. Ongoing medication costs vary widely depending on drugs required and dog size. Regular monitoring adds periodic examination and testing costs. Pet insurance obtained before murmur detection can provide valuable coverage for cardiac workup and ongoing management costs that may arise.

Prevention of heart murmurs focuses on preventing the underlying cardiac conditions that cause them, where possible. Year-round heartworm prevention eliminates this entirely preventable cause of cardiac damage and murmurs. Maintaining excellent dental health reduces the risk of bacteremia that could cause infective endocarditis and valve damage. Feeding appropriate, high-quality diets supports overall cardiovascular health. For predisposed breeds, awareness of genetic risk and appropriate breeding practices can reduce population-level incidence of inherited cardiac conditions. However, many causes of heart murmurs, including degenerative valve disease in predisposed breeds, cannot currently be prevented despite these measures.

Lifestyle modifications for dogs with heart murmurs depend on whether underlying disease requires management. Dogs with innocent murmurs or murmurs without significant underlying disease require no lifestyle changes. Dogs with progressive cardiac disease benefit from maintaining a healthy body weight to reduce cardiovascular workload, moderate exercise appropriate to their cardiac tolerance, avoiding excessive heat or humidity that stresses the cardiovascular system, and stress reduction where possible. Dietary modifications including sodium restriction may be recommended for dogs with heart disease. These adjustments become more important as disease progresses and help maintain quality of life while managing cardiac function.

Regular monitoring represents the cornerstone of managing dogs with heart murmurs of uncertain or progressive significance. Schedule veterinary examinations at intervals appropriate to your dog's diagnosis and disease stage, which may range from every few months to annually. Learn to monitor your dog's resting respiratory rate at home, counting breaths per minute during sleep or quiet rest, and track this number over time. Report increases to your veterinarian, as rising respiratory rate often indicates fluid accumulation before other symptoms develop. Watch for subtle changes in energy level, exercise tolerance, coughing patterns, or breathing effort. Keeping records of observations helps identify trends and supports discussions with your veterinary team.

Long-term management for dogs with clinically significant murmurs and underlying heart disease requires commitment to treatment protocols and ongoing veterinary partnership. Administer all prescribed medications consistently and at appropriate times. Maintain recommended dietary modifications. Keep all monitoring appointments and be prepared for treatment adjustments as disease progresses. Understand that most acquired heart diseases are progressive, and management goals evolve from maintaining normal function to controlling symptoms and preserving quality of life. Open communication with your veterinary team about your dog's condition, your observations, and your goals for care ensures the best outcomes throughout your dog's life with heart disease.

Support resources for managing dogs with heart murmurs and cardiac disease include veterinary cardiologists who provide specialized expertise in diagnosis and management. Your primary care veterinarian coordinates overall care and can guide decisions about specialist referral. The Veterinary Cardiovascular Society and American College of Veterinary Internal Medicine maintain resources for pet owners. Online communities of owners managing cardiac disease in their dogs offer practical support and shared experience. Breed clubs for predisposed breeds often provide information about cardiac screening recommendations and disease prevalence. These resources complement veterinary guidance to help you navigate your dog's cardiac health effectively.

Emergency veterinary care is required if your dog with a known heart murmur develops sudden severe breathing difficulty, collapses or faints, has gums that appear blue or white rather than pink, cannot settle or rest due to breathing distress, or shows sudden dramatic changes in condition. These signs indicate acute cardiac decompensation requiring immediate intervention. Even if previous evaluations suggested the murmur was not causing problems, acute changes can occur and warrant emergency attention. When in doubt about the severity of symptoms, err on the side of seeking emergency evaluation, as rapid treatment of cardiac emergencies can be lifesaving.

Urgent same-day veterinary visits are appropriate when dogs with heart murmurs develop concerning symptoms that do not constitute immediate emergencies. New or significantly worsened coughing deserves prompt attention, as it may indicate heart enlargement or fluid accumulation. Noticeable increases in breathing rate or effort at rest, even without severe distress, warrant same-day evaluation. Decreased appetite, unusual lethargy, or obvious reduction in exercise tolerance suggests possible disease progression. Any new symptoms in a dog with a previously stable murmur should be evaluated promptly to determine whether intervention is needed.

Routine veterinary appointments should be maintained for recommended monitoring of heart murmurs. Puppies with suspected innocent murmurs should return for recheck examination at the interval suggested by your veterinarian to confirm murmur resolution. Adult dogs with murmurs warrant periodic reevaluation even if asymptomatic, with frequency depending on the suspected underlying cause and any diagnostic findings. Dogs receiving cardiac medications need regular rechecks to assess response and adjust treatment. Schedule appointments when questions arise about your dog's cardiac status, prognosis, or management. Keep your veterinarian informed about any changes you observe at home, even if subtle.

Trusting your observations about your dog's condition serves them well, especially when you know they have a heart murmur that might indicate underlying cardiac disease. You see your dog daily and can detect subtle changes in energy, breathing, behavior, or exercise tolerance that might be missed on periodic veterinary examination. If your dog seems different in ways that concern you, professional evaluation is appropriate even if you cannot specifically define what seems wrong. Heart disease often progresses gradually, and the changes owners notice frequently reflect meaningful disease advancement. Seeking veterinary guidance when you have concerns is always appropriate, as early intervention when disease progresses can improve both length and quality of your dog's life.