Heart Murmur in Dogs: Everything You Need to Know

When it comes to our furry friends, their health and well-being should always be a priority. That’s why it’s crucial to pay attention to any signs or symptoms that may indicate an underlying issue. One such concern is a heart murmur in dogs. While some heart murmurs are harmless, others can be quite serious. In this article, we will explore the causes, symptoms, diagnosis, and treatment options for heart murmurs in dogs.

Every time I perform a physical examination on one of my patients, I make sure to listen carefully to their heart and lungs. It’s an essential part of the exam and a valuable tool in protecting your dog’s health. Ideally, I hope to hear the reassuring “lub-dub” sound, ensuring everything sounds great. However, finding a heart murmur during a routine check-up can be a game-changer. By detecting it early, we can take proactive steps to determine the cause and establish the best course of action. Neglecting a heart murmur could lead to serious issues down the line, making it harder to treat. That’s why regular wellness exams are crucial for your dog’s overall health.

Understanding Heart Murmurs

Typically, when a veterinarian listens to a dog’s heart with a stethoscope, they hear a crisp and clear sound. However, sometimes, they may detect an abnormal “whoosh” sound overlaid on the heartbeat. This sound is what we call a heart murmur.

To understand heart murmurs, it’s essential to have a basic understanding of the heart’s structure. The heart consists of four chambers: the right atrium, right ventricle, left atrium, and left ventricle. These chambers are separated by small heart valves that open and close, depending on whether the chambers are pumping or filling with blood. Pressure gradients within the heart, along with these valves, ensure that blood flows in the correct direction.

Blood returns to the heart after delivering oxygen to the body. It enters the right atrium, passes through the tricuspid valve into the right ventricle, and then gets pumped through the pulmonic valve into the main pulmonary artery, leading to the lungs. In the lungs, the blood picks up oxygen. From there, it flows through the pulmonary veins into the left atrium, through the mitral valve, and into the left ventricle. Finally, the left ventricle pumps the oxygenated blood through the aortic valve and into the aorta, which distributes it to the rest of the body.

Causes of Heart Murmurs

Heart murmurs occur due to turbulent blood flow within the heart. This turbulence can be caused by various factors, such as blood flowing backward through a leaky valve, being forced through a narrowed valve, or passing through an abnormal hole or vessel connection in the heart. Sometimes, thin and watery blood can also alter the flow dynamics, resulting in a murmur.

Classification of Heart Murmurs

Heart murmurs can be categorized based on their intensity, location, and timing. The intensity of a murmur is graded on a scale from one to six:

  • Grade I: Very faint and requires careful listening in a quiet room.
  • Grade II: Soft but consistent.
  • Grade III: Moderate in intensity and easy to hear.
  • Grade IV: Loud, but without a palpable thrill (a vibration in the chest wall caused by turbulent blood flow).
  • Grade V: Loud, with a palpable thrill.
  • Grade VI: Loud enough to be heard without a stethoscope on the chest wall, with a palpable thrill.
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Additionally, murmurs can be classified based on their location and when they occur. The location indicates where in the heart the murmur is loudest. Murmurs can be systolic (heard when the heart is contracting) or diastolic (heard when the heart is relaxed and filling). Some murmurs are continuous, meaning they are audible all the time.

Common Causes of Heart Murmurs

Since heart murmurs are auditory evidence of turbulent blood flow within the heart, there can be many underlying conditions responsible for their presence. Let’s explore some of the most common causes:

Innocent Murmurs

In young puppies, heart murmurs can be physiologic and may occur due to normal processes within the heart. Innocent murmurs are usually harmless and are often seen in rapidly growing or large breed puppies. They tend to go away on their own after a few weeks. However, if a veterinarian suspects an innocent murmur, they will monitor the pup and reevaluate during subsequent visits.

Anxiety-Related Murmurs

Stressed or anxious dogs may develop heart murmurs due to an accelerated heart rate. Like innocent murmurs, anxiety-related murmurs typically resolve on their own. If your dog experiences stress during vet visits, consider seeking advice from your veterinary team to alleviate their fear and anxiety. In some cases, anxiety-reducing medications like gabapentin may be prescribed.

Anemia or Low Protein

Underlying illnesses such as anemia (low red blood cell count) or low blood protein can lead to functional heart murmurs. These murmurs occur even in the absence of heart disease and usually resolve once the underlying condition is treated.

Heart Disease

Structural damage to the heart muscle or valves can cause murmurs. Heart disease in dogs can be congenital (present at birth), inherited (genetically linked), or acquired over time.

  • Heart disease in puppies:

    • Patent ductus arteriosus (PDA): This is an abnormal connection between the aorta and pulmonary artery that should have closed at birth. It causes continuous blood flow from the aorta to the pulmonary artery, resulting in a continuous murmur.
    • Pulmonic stenosis: Narrowing of the pulmonic valve makes the heart work harder to pump blood through the restricted opening.
    • Subaortic stenosis: Narrowing at the base of the aortic valve increases the workload of the heart.
  • Heart disease in adult or senior dogs:

    • Mitral valve disease: The mitral valve, and sometimes the tricuspid valve, become wrinkly and misshapen in older small breed dogs. This prevents the valve from closing tightly, causing blood to flow back from the ventricle to the atrium, resulting in a murmur.
    • Dilated cardiomyopathy (DCM): The walls of the heart, especially the ventricles, become thin and weak, leading to ineffective blood pumping. Some breeds may have a genetic predisposition to DCM, and there is ongoing research into potential dietary links.
    • Heartworm disease: Adult heartworms reside in the right side of the heart and pulmonary artery, interfering with heart valve function and potentially causing a heart murmur.

It’s important to note that the intensity of a murmur doesn’t always correlate with the severity of the disease. While dogs with mitral valve disease tend to have louder murmurs as the disease progresses, the severity of the disease may not be evident until much later. On the other hand, dogs with DCM may have faint murmurs or no murmurs at all, even with significant heart failure.

Congestive Heart Failure

Over time, heart diseases can lead to congestive heart failure (CHF). CHF occurs when the heart cannot efficiently pump enough blood to meet the body’s demands. It can cause problems with blood pressure and result in fluid buildup in the abdomen or chest cavity.

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Recognizing the Symptoms

In some cases, a heart murmur may go unnoticed unless a veterinarian detects it during a physical exam. For murmurs with a grade IV or higher intensity, you may be able to feel a palpable vibration when placing your hand on your dog’s chest. Additionally, arrhythmias (abnormal heart rhythms) can be detected by feeling your dog’s chest. Normal heartbeats should have a steady and consistent pattern of “lub-dub.” If you notice extra beats or abnormal patterns, it may indicate heart disease, and you should contact your veterinarian.

Other signs of heart problems to watch out for include lethargy, weakness, exercise intolerance, weak pulses, coughing (especially at night), increased rate or effort of breathing, unwillingness to lie down, weight loss, lack of appetite, and a pendulous abdomen. If you observe any of these signs, it’s essential to make an appointment with your veterinarian.

Certain signs may indicate a life-threatening situation, such as pale or blue gums, acute collapse, abnormal posture with elbows winged out and neck outstretched, or respiratory distress. If your dog exhibits any of these signs, it is crucial to seek immediate veterinary care.

Diagnosing Heart Murmurs

A veterinarian will listen carefully to your dog’s heart in a quiet room to diagnose a heart murmur. It’s easier to detect murmurs when your dog is calm and not shaking or panting. Depending on your dog’s age, medical history, and the intensity of the murmur, your veterinarian may recommend additional diagnostic tests, including blood and urine tests to check for anemia or low blood protein levels, blood pressure measurement, electrocardiogram (EKG) to evaluate heart rate and rhythm, chest X-rays to assess heart size and shape, and an echocardiogram (ultrasound of the heart) to evaluate heart function, blood flow, and overall anatomy. Some veterinary clinics provide echocardiograms, while others may refer you to a veterinary cardiologist for more specialized care.

Treatment Options

The appropriate treatment for a heart murmur in dogs depends on the underlying cause and the results of diagnostic testing. Functional murmurs typically resolve with the treatment of any underlying conditions, such as anemia or low protein levels. Innocent murmurs and stress/anxiety-related murmurs tend to go away on their own. Dogs with heartworm disease will require treatment to eliminate the heartworms.

Surgical options are available for young dogs with certain heart conditions. For example, a veterinary surgeon can close a patent ductus arteriosus (PDA) to redirect blood flow. In some cases, surgical interventions can lead to the resolution or improvement of the murmur.

However, some murmurs caused by structural abnormalities may persist throughout a dog’s life. Older dogs with mitral valve disease, for instance, will always have a murmur that becomes louder over time. In such cases, the focus shifts to supporting the dog’s heart function and managing congestive heart failure for as long as possible. Numerous medications are available to improve heart function, manage arrhythmias, high blood pressure, and fluid accumulation. In severe cases, pacemaker implantation may be necessary. Additionally, Omega-3 essential fatty acid supplements may be recommended to support heart health.

The “Heart” of Heart Murmurs

While a heart murmur diagnosis might be concerning, there is good news. Many dogs with heart murmurs can live long, happy lives. The key is to bring your dog for regular wellness visits, ideally at least once a year, or more frequently for senior dogs. These visits significantly increase the chances of detecting a murmur before it becomes problematic. Follow your veterinarian’s recommendations for additional testing, and work together to create a monitoring and treatment plan. Early intervention plays a crucial role in minimizing heart disease symptoms and delaying the onset of congestive heart failure.

If your dog has a heart murmur, we’d love to hear about your experiences. Please feel free to share your stories below.

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