Heart Murmurs in Dogs: Causes, Symptoms & Treatment

Heart Murmurs in Dogs: A Comprehensive Guide

A heart murmur is an abnormal sound detected during a heartbeat that may indicate underlying heart conditions or, in some cases, be a harmless variation in blood flow. When your veterinarian listens to your dog’s heart with a stethoscope during a routine examination, they may detect a whooshing or swishing sound that differs from the normal heartbeat. This sound occurs when blood isn’t flowing smoothly through the heart chambers and valves. While some heart murmurs are benign and resolve on their own, others may signal serious cardiac disease requiring immediate attention and ongoing management. Understanding what heart murmurs are, their causes, and available treatment options can help you make informed decisions about your dog’s health and quality of life.

What Causes Heart Murmurs in Dogs?

Heart murmurs in dogs can develop for various reasons, ranging from congenital conditions present at birth to acquired diseases that develop later in life. Understanding the underlying cause is essential for determining the appropriate treatment approach and prognosis for your pet.

Congenital Heart Defects

Some dogs are born with heart defects that cause murmurs from birth. These congenital conditions are present from the moment of conception and may be inherited or develop during fetal development. Common congenital heart defects include:

• Patent Ductus Arteriosus (PDA): A blood vessel that remains open after birth instead of closing naturally, allowing blood to bypass normal circulation patterns.
• Pulmonic Stenosis: A narrowing of the pulmonary valve that restricts blood flow to the lungs, forcing the heart to work harder to pump blood.
• Subaortic Stenosis: Fibromuscular narrowing below the aortic valve, making it difficult for blood to leave the heart and enter systemic circulation.
• Ventricular Septal Defect: An abnormal opening in the wall between the lower heart chambers, allowing blood to flow between them incorrectly.
• Tricuspid Valve Dysplasia: An abnormally formed tricuspid valve that fails to seal properly, causing blood to leak backward.

Acquired Heart Conditions

Many dogs develop heart murmurs later in life due to acquired heart disease. These conditions develop over time and are often related to degenerative processes or other medical conditions.

Mitral Valve Disease (MVD): This is the most common cause of heart murmurs in dogs, particularly in small breeds. Mitral valve disease, also known as chronic valve disease, degenerative mitral valve disease, or endocardiosis, occurs when the mitral valve—located between the left atrium and left ventricle—begins to degenerate with age. The valve normally allows blood to flow from the left atrium to the left ventricle but prevents backflow. As dogs age, this valve deteriorates, causing blood to leak backward into the left atrium. This progressive condition is especially common in older dogs and certain breeds like Cavalier King Charles Spaniels, which may have a genetic predisposition.

Dilated Cardiomyopathy (DCM): This disease is more commonly seen in larger breed dogs and causes the heart muscle to weaken, resulting in an enlarged heart and reduced contraction strength. Dilated cardiomyopathy often leads to a secondary leaky mitral valve, creating murmurs and reducing the heart’s ability to pump blood efficiently throughout the body.

Heartworm Disease: A parasitic infection transmitted through mosquito bites, heartworm disease can cause significant damage to the heart and lungs, leading to heart murmurs and other serious complications.

Other Causes

Several other conditions can cause heart murmurs in dogs. Bacterial infection of the heart valves, known as endocarditis, occurs when bacteria enter the bloodstream from sources such as wounds or dental disease and infect the valve tissue. Additional causes include anemia, hyperthyroidism, aortic stenosis, and various valve infections or defects. In some cases, innocent murmurs may develop from rapid growth, stress, or excitement, particularly in young dogs.

Types of Heart Murmurs

Heart murmurs are classified based on when they occur during the cardiac cycle and their associated conditions. Your veterinarian will determine the specific type during examination.

Systolic Heart Murmurs

Systolic murmurs occur during the heart’s contraction phase when the ventricles squeeze to push blood out. These are associated with conditions including heartworm disease, hyperthyroidism, anemia, valve endocarditis, aortic stenosis, and various valve dysplasias and defects.

Diastolic Heart Murmurs

Diastolic murmurs occur during the relaxation phase of the heartbeat. These may indicate aortic and pulmonic valve endocarditis or mitral and tricuspid valve stenosis.

Continuous or To-and-Fro Heart Murmurs

These murmurs are heard throughout the cardiac cycle and may be associated with aortic stenosis combined with aortic regurgitation, ventricular septal defects with aortic regurgitation, or patent ductus arteriosus.

Symptoms and Signs of Heart Murmurs

Many dogs with heart murmurs show no visible symptoms, especially in early stages. However, as the condition progresses, your dog may display various clinical signs indicating declining heart function. Watch for these common symptoms:

• Persistent coughing, particularly when resting or at night
• Difficulty breathing or rapid breathing patterns
• Fatigue and lethargy during normal activities
• Weakness or episodes of collapse
• Loss of appetite or poor appetite
• Fainting or syncope episodes
• Reduced exercise tolerance compared to previous abilities

If your dog exhibits any of these symptoms, contact your veterinarian promptly for evaluation. Innocent murmurs typically produce no symptoms and resolve on their own as the dog matures or the underlying condition resolves.

Diagnosis of Heart Murmurs

Your veterinarian will begin by listening to your dog’s heart with a stethoscope during a physical examination. If a murmur is detected, further diagnostic testing helps identify the underlying cause and severity. Common diagnostic procedures include:

Echocardiography (Ultrasound): This non-invasive imaging technique uses sound waves to create detailed pictures of the heart’s structure and function, allowing veterinarians to visualize valve problems, chamber enlargement, and blood flow patterns.

Electrocardiography (ECG): This test records the electrical activity of the heart to detect abnormal rhythms or signs of heart disease.

Chest X-rays: Radiographs reveal the heart’s size and shape, helping identify enlargement or fluid buildup in the lungs.

Blood Tests: Laboratory work may be performed to assess kidney function, hormone levels, and detect infections or other systemic conditions contributing to the murmur.

Treatment Options for Heart Murmurs

Treatment for heart murmurs depends primarily on the underlying cause and severity of the condition. Your veterinarian or a veterinary cardiologist will develop a customized treatment plan based on your dog’s specific diagnosis.

Innocent Murmurs

Innocent murmurs require no treatment but typically necessitate follow-up appointments to ensure they resolve naturally as the dog matures. Your veterinarian will monitor the murmur during routine check-ups to confirm it persists without progression.

Medication Management

For dogs with heart disease-related murmurs, several medication classes help manage symptoms and improve cardiac function:

Diuretics: These medications improve the kidney’s ability to remove excess water from the body and enhance blood flow. Furosemide is commonly prescribed to prevent fluid accumulation in the lungs.

Angiotensin-Converting Enzyme (ACE) Inhibitors: Medications like benazepril and enalapril open blood vessels and decrease fluid retention, promoting smoother blood flow and reducing the heart’s workload.

Inodilators: Pimobendan improves the heart muscle’s ability to contract and relaxes blood vessels, allowing blood to flow more easily throughout the body.

Beta-Blockers: These medications help regulate heart rate and rhythm, reducing stress on the heart.

Dietary Management

A specialized diet can support heart health in dogs with murmurs. Your veterinarian may recommend high-quality diets formulated for cardiac support, potentially reduced sodium content to decrease fluid retention, and appropriate caloric intake to maintain healthy weight.

Surgical Interventions

For certain congenital heart defects like PDA or pulmonic stenosis, surgical procedures or catheter-based interventions may be recommended to correct the structural abnormality. Your cardiologist can discuss specific surgical and palliative options available for your dog’s condition.

Lifestyle Modifications

Dogs with heart murmurs benefit from lifestyle adjustments that reduce cardiac stress:

• Maintaining a healthy weight to reduce strain on the heart
• Providing regular, moderate exercise appropriate for your dog’s condition
• Avoiding excessive exertion or stressful situations
• Keeping the environment calm and stress-free
• Managing dental health to prevent bacterial infections

Monitoring and Prognosis

Dogs with heart murmurs require ongoing veterinary monitoring to track disease progression and adjust treatment as needed. At minimum, your dog will require veterinary visits every six months to monitor the murmur’s status. Depending on your dog’s condition, these visits may include repeat echocardiograms and X-rays to assess cardiac function and detect complications early. Regular follow-up care is essential for maintaining quality of life and ensuring timely adjustments to the treatment plan.

The prognosis for dogs with heart murmurs varies considerably depending on the underlying cause, severity, your dog’s age, and response to treatment. Innocent murmurs generally carry an excellent prognosis, while murmurs associated with significant heart disease require lifelong management. With appropriate treatment and monitoring, many dogs with cardiac disease can maintain a good quality of life for extended periods.

Frequently Asked Questions

Q: What is the difference between an innocent murmur and a pathological murmur?

A: Innocent murmurs are benign variations in blood flow that don’t indicate structural heart disease and often resolve without treatment. Pathological murmurs result from underlying heart disease or defects and typically require diagnosis and management to prevent complications.

Q: Can heart murmurs in dogs be prevented?

A: While congenital heart defects cannot be prevented, acquired heart disease risks may be reduced through maintaining healthy weight, regular exercise, dental care to prevent infections, and heartworm prevention medication in endemic areas.

Q: How long can a dog live with a heart murmur?

A: Lifespan varies significantly based on the cause and severity of the murmur. Some dogs with well-managed heart disease live for years with good quality of life, while prognosis for severe conditions may be shorter. Your veterinarian can provide specific expectations for your dog’s situation.

Q: Is a heart murmur in a young dog always concerning?

A: Not necessarily. Young dogs may have innocent murmurs related to rapid growth that resolve as they mature. However, any murmur detected in a young dog warrants evaluation to rule out congenital heart defects or other conditions requiring early intervention.

Q: What should I do if my veterinarian detects a heart murmur?

A: Schedule further diagnostic testing as recommended, such as echocardiography, to determine the cause and severity. Work with your veterinarian to develop an appropriate monitoring and treatment plan tailored to your dog’s specific condition and needs.

Conclusion

Heart murmurs in dogs range from benign findings that require only monitoring to serious conditions necessitating comprehensive medical management. Early detection through regular veterinary examinations and proper diagnosis through appropriate testing are crucial for optimal outcomes. By understanding the causes, recognizing symptoms, and working closely with your veterinarian to implement an appropriate treatment and monitoring plan, you can help ensure your dog maintains the best possible quality of life. If you suspect your dog may have a heart murmur or have noticed symptoms of cardiac disease, contact your veterinarian promptly to discuss evaluation and care options.

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medha deb

 

Medha Deb is an editor with a master's degree in Applied Linguistics from the University of Hyderabad. She believes that her qualification has helped her develop a deep understanding of language and its application in various contexts.

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