Understanding Canine Heart Murmurs: Causes, Symptoms, and Treatment

Heart Murmur in Dogs

Hearing that your dog has a heart murmur might sound scary at first. However, with a little knowledge and the proper care, many dogs can live happy, healthy lives despite having one. A heart murmur isn’t a disease itself—it’s more like a clue, a sound that indicates how well the heart is functioning. So, what exactly is a heart murmur, and what does it mean for your beloved pup? We will explore heart murmurs in dogs, including causes, diagnosis, grading, treatment, and the importance of veterinary check-ups.

What Is a Heart Murmur?

Simply put, a heart murmur is an abnormal sound heard when a veterinarian listens to your dog’s heart with a stethoscope. A murmur creates a whooshing or swishing noise instead of the usual steady “lub-dub” rhythm. This sound is caused by turbulent blood flow within the heart or surrounding blood vessels.

Heart murmurs can vary in intensity, and veterinarians classify them into grades (1 through 6), with grade 1 being the softest and grade 6 being the loudest. Think of it like background noise—sometimes it’s barely noticeable. At the same time, other times it can dominate the sound of a heartbeat.

The Heart's Compartments

At the core of the matter, a dog’s heart contains four chambers: two atria and two ventricles. Maintaining blood flow is crucial, and these compartments play a significant role in achieving it.

Within these chambers lie the unsung heroes of the canine cardiovascular system – the heart valves. Their duty is to ensure the smooth, one-way flow of blood. But sometimes, even guardians can falter. We’ll investigate how valve abnormalities can lead to the murmurs that capture our attention.

Beyond the heart’s chambers, a network of blood vessels transports the life-giving fluid to every nook and cranny of a dog’s body. When these vessels face turbulence, it can manifest as a murmur.

Not all heart murmurs are created equal. Some are innocent, like a gentle breeze rustling through leaves, while others hint at underlying health issues. Understanding the difference is key to your dog’s well-being.

Grading Heart Murmurs: From Soft Whispers to Loud Roars

The volume of a heart murmur can vary greatly. Veterinarians use a grading system to classify the intensity of murmurs, from barely audible whispers to thunderous roars. This article will simplify the grading system and explain its implications for your beloved pet.

Heart murmurs in dogs are graded on a scale from I to VI, with each grade indicating the intensity and audibility of the murmur. These grades are essential to diagnosing and assessing the severity of the underlying heart condition. Here’s a breakdown of each grade:

Grade I: A grade I heart murmur is the softest and barely audible with a stethoscope. It may not be present during every examination and is often difficult to detect. These murmurs are typically harmless and may not indicate any significant heart issues. They are sometimes called “innocent” murmurs commonly found in puppies.
Grade II: A grade II heart murmur is still relatively soft but more consistently present during examinations. It’s audible without much difficulty and may or may not indicate an underlying problem. Many grade II murmurs are still considered innocent, especially in young dogs.
Grade III: Grade III murmurs are louder and easier to hear. They often suggest an underlying heart issue, such as a valve problem or other structural abnormalities. Further diagnostic tests, like echocardiograms, are typically recommended to determine the cause and severity of the murmur.
Grade IV: Grade IV murmurs are even louder and can be heard without a stethoscope. These murmurs are often associated with more significant heart problems, and dogs with grade IV murmurs usually require further evaluation and treatment.
Grade V: A grade V heart murmur is easily audible over a large area of the chest. These murmurs often indicate severe heart disease or structural defects that require prompt attention and treatment.
Grade VI: The loudest of all, a grade VI heart murmur is heard over a large portion of the chest and can also be felt through the chest wall. Dogs with grade VI murmurs are in critical condition and need immediate veterinary intervention.

It’s crucial to note that the grade of the murmur is just one aspect of diagnosing and assessing heart conditions in dogs. Additional tests, such as radiographs, electrocardiograms (ECG or EKG), and echocardiograms, may be required to determine the underlying cause and create a proper treatment plan. Regular follow-up appointments with a veterinarian are essential for monitoring the progression of heart murmurs and adjusting treatment as needed to ensure the best possible care for your furry companion.

What Causes a Heart Murmur?

There are several reasons why a dog might have a heart murmur. Some are harmless, while others may require treatment. Here are the most common causes:

Innocent (or Functional) Murmurs: Puppies and young dogs sometimes develop murmurs that they outgrow as they mature. These are harmless and usually disappear by the time the dog is a year old.
Structural Issues: Some dogs have congenital heart defects, meaning they were born with an abnormality in the heart’s structure. This could include narrowed blood vessels or a heart valve that doesn’t close properly, causing blood to flow irregularly.
Acquired Conditions: Older dogs may develop heart murmurs due to conditions such as valve disease or cardiomyopathy (a weakened heart muscle). These conditions can cause blood to leak or struggle to circulate efficiently.
Anemia or Other Health Problems: In some cases, conditions like anemia (low red blood cell count) or hyperthyroidism can cause a murmur. Treating the underlying issue may reduce or eliminate the murmur.

Types of Heart Murmur

Systolic Heart Murmurs:
- Aortic Stenosis (AS): This heart defect occurs when the aortic valve narrows, obstructing blood flow in dogs. The resulting turbulence in blood flow creates a systolic murmur. Severity varies, and dogs may remain asymptomatic or develop heart failure over time.
- Pulmonic Stenosis (PS): Like aortic stenosis, pulmonic stenosis involves narrowing the pulmonary valve, leading to a systolic murmur. Dogs with PS may exhibit symptoms such as exercise intolerance and fainting.
- Mitral Valve Insufficiency (MVI): This is a common acquired heart condition in older dogs, particularly small breeds like the Cavalier King Charles Spaniel. It involves improperly closing the mitral valve during systole, allowing blood to flow backward into the left atrium. This regurgitation creates a systolic murmur. Symptoms may include coughing, exercise intolerance, and fluid accumulation in the lungs.
Diastolic Heart Murmurs:
- Aortic Regurgitation (AR): A diastolic murmur occurs when the aortic valve fails to close correctly, causing blood to pour back into the left ventricle during the heart’s relaxation phase, called diastole. This condition can be present at birth or acquired and is often associated with other heart diseases.
- Mitral Valve Stenosis (MVS): MVS involves narrowing the mitral valve, restricting blood flow from the left atrium to the left ventricle during diastole. Diastolic murmurs may result from this condition, and affected dogs may display symptoms like exercise intolerance and fluid retention.
Continuous Heart Murmurs:
- Patent Ductus Arteriosus (PDA): A continuous heart murmur is characteristic of PDA, a congenital defect where the ductus arteriosus, a fetal blood vessel, fails to close after birth. This results in continuous turbulent blood flow between the aorta and pulmonary artery. PDA typically requires surgical intervention for closure.
Innocent (Functional) Heart Murmurs:
- Physiological Murmurs: These murmurs are often heard in young, healthy puppies and canines during rapid growth or excitement. They are considered innocent and usually resolve as the dog matures.
Dynamic Heart Murmurs:
- Dynamic Subaortic Stenosis (DSS): This condition involves a dynamic obstruction of blood flow beneath the aortic valve, which can lead to systolic murmurs. DSS often occurs in specific breeds and may worsen with exercise.
Structural Heart Murmurs:
- Ventricular Septal Defect (VSD): VSD is a congenital heart defect characterized by a septum (wall) hole between the heart’s ventricles. Blood flows abnormally from the left to the right ventricle, causing a murmur. Treatment may be necessary depending on the size and severity of the defect.
  Understanding the type of heart murmur your dog has is crucial for proper diagnosis and treatment. Your veterinarian will run a combination of physical examination, auscultation, and diagnostic tests like echocardiography to determine the specific type, grade, and underlying cause of the murmur. Treatments depend on the heart condition’s type and severity, ranging from medication to surgical interventions. Regular monitoring and collaboration with your veterinarian are essential to ensure the best care for your furry companion

What Symptoms Should I Watch For?

While many dogs with heart murmurs show no symptoms, it’s important to stay alert for signs that their heart may be struggling. Symptoms to look out for include:

Fatigue or lethargy (your dog tires easily during play or walks)
Coughing, especially at night or after activity
Shortness of breath or rapid breathing
Fainting or collapse (in severe cases)
Decreased appetite or weight loss

If you notice any of these signs, contact your veterinarian. Early detection and treatment can help prevent more serious complications.

Heart Murmur Treatment Options

Treatment options for dog heart murmurs vary based on underlying conditions.

Medications:
- Diuretics: These medications, like furosemide (Lasix), help remove excess fluid from the body, reducing the workload on the heart and alleviating symptoms like coughing and fluid retention.
- ACE Inhibitors: Drugs like enalapril (Enacard) or benazepril (Fortekor) can dilate blood vessels, lower blood pressure, and reduce the strain on the heart.
- Beta-Blockers: Medications such as atenolol (Tenormin) can slow the heart rate and decrease its workload, making them useful in some instances.
- Vasodilators: These drugs relax blood vessels, making it easier for the heart to pump blood. They are often used in cases of aortic or pulmonic stenosis.
Surgical Interventions:
- Balloon Valvuloplasty: This procedure is used to treat valvular stenosis by inserting a catheter with a balloon into the narrowed valve and inflating it to widen the opening.
- Valve Repair or Replacement: Surgery may involve repairing or replacing the damaged valve for severe mitral valve disease.
- Patent Ductus Arteriosus (PDA) Closure: PDA is often treated surgically by closing the abnormal blood vessel using devices or ligation.

Lifestyle Adjustments for Dog with Heart Murmur

After diagnosis, the journey continues with vigilant monitoring. Regular check-ups and tests help track your dog’s progress and adjust treatment plans accordingly. Ultimately, the goal is to ensure your furry companion enjoys a happy and fulfilling life despite a heart murmur.

Dietary Changes: A heart-healthy diet with reduced sodium content can help manage symptoms and fluid retention.
Follow your veterinarian’s instructions meticulously when giving prescribed medications. Consistency is crucial for managing symptoms and maintaining heart health.
Exercise Restrictions: Limiting strenuous exercise can prevent the heart from working too hard and exacerbating the condition.
Weight Management: Maintaining a healthy weight is crucial to reducing the strain on the heart, especially for overweight dogs.
Stress Reduction: Minimizing stress and anxiety can benefit dogs with heart murmurs.
Routine check-ups with your veterinarian are essential to monitor the progression of the heart condition and adjust treatment as needed.
Follow-up appointments may include echocardiograms and blood tests to assess the effectiveness of medication and the heart’s overall health.
Create a peaceful and stress-free environment at home. Dogs with heart murmurs may benefit from reduced noise and commotion.
Maintain a journal of your dog’s behaviour, appetite, and any changes in their condition. This can help you and your veterinarian track any developments.
Spend quality time with your dog. The emotional bond you share can positively impact their overall well-being.
Sometimes, heart murmurs may progress, and end-of-life decisions may become necessary. Consult with your veterinarian to discuss humane and compassionate options when the time comes.

Finding Support and Resources

Canine Cardiology Organizations: Knowledge and support are your best allies in your journey with a dog who has a heart murmur. Explore the valuable resources provided by canine cardiology organizations. These experts are here to guide you through the maze of information and care.
Online Communities: In the age of the internet, connecting with fellow dog owners facing similar challenges has always been challenging. Online communities provide a safe space to share stories, ask questions, and gain insights.
Supportive Literature: Books and literature on canine heart health can be a treasure trove of information and guidance. Discover the written resources to help you become a more informed and confident caregiver.
When to Seek a Second Opinion: In the world of healthcare, second opinions can offer invaluable perspectives.
Expert Consultation: For challenging and intricate cases, consultation with veterinary specialists may be necessary.
Holistic Approaches: Traditional veterinary care is not the only path. Discover the world of alternative therapies and holistic approaches that can complement conventional treatments, enhancing your dog’s well-being.
Integrating Holistic Practices with Veterinary Care: Harmony can exist between traditional and holistic approaches. Learn how to strike a balance that best suits your dog’s needs, embracing a holistic perspective while maintaining the support of modern medicine.

Hearing that your dog has a heart murmur can feel overwhelming at first. Still, it’s important to remember that many dogs live long and joyful lives with this condition. Understanding what a heart murmur is and getting the help needed can help your dog stay healthy, active, and full of love.