Overview

Severity: Medium - High
Life stage: All
  • A dog heart murmur is caused by irregular blood flow through the heart. It creates an abnormal sound.
  • Veterinarians grade murmurs from 1-6, based on the intensity.
  • Many dogs with heart murmurs have no other symptoms. Sometimes a murmur can signify heart disease.
  • Treatment is directed at correcting or managing the underlying disease.

When your dog visits the veterinary clinic for his annual wellness exam, one of the most important things your veterinarian will do is listen to your dog’s chest with a stethoscope. The sound of your dog’s heart and lungs can give your veterinarian a lot of information and can even be an early warning sign of illness long before external symptoms appear. 

Heart murmurs are one of the common sounds your veterinarian will try to detect when listening to your dog’s heart.

What is a Dog Heart Murmur?

A normal heart is often described as making a rhythmic “lub-dub” sound. The first “lub” sound occurs when the first pair of heart valves—called the atrioventricular valves—close as the heart muscle contracts. The second “dub” sound occurs when the second pair of heart valves—called the semilunar valves—close and the heart muscle relaxes. 

A heart murmur is an abnormal sound that can occur before, after, or during these normal “lub-dub” sounds. The murmur is caused by irregular or turbulent blood flow through the heart. The exact timing and sound of the murmur can vary depending on the underlying disease. 

Some murmurs make a whooshing sound, while others may make a clicking noise, or even a high-pitched, almost musical sound. 

Veterinarians classify heart murmurs based on their timing relative to the normal heart sounds, their loudness, and the point of maximal intensity—the area of the chest where the murmur is heard most clearly. These classifications can help the veterinarian identify the underlying cause of the murmur.

Heart Murmur Grades in Dogs

veterinarian grading dog heart murmur

If your dog is diagnosed with a heart murmur, your veterinarian may assign the murmur a numerical grade. The grade of murmur is a useful classification tool and can also be used to monitor any changes in your dog’s heart murmur over time. Heart murmurs are graded on a scale of 1-6, depending on the loudness of the murmur.

Heart Murmur Grade Characteristics 
Grade 1 A low-intensity murmur that can only be heard with careful listening in a quiet environment.
Grade 2 A quiet murmur that is immediately noticeable when the stethoscope is placed over the point of maximal intensity.
Grade 3 A moderately loud murmur.
Grade 4 A loud murmur that can easily be heard over several areas of the chest.
Grade 5 A very loud murmur that is palpable—meaning the veterinarian can feel it when placing a hand on the dog’s chest.
Grade 6 A palpable murmur that can be heard even with the stethoscope held slightly away from the dog’s chest.

It is very important to remember that heart murmur grade is ONLY a measure of how loud the murmur is and does not necessarily correlate to the severity of the underlying disease. 

Some low-grade murmurs can be life-threatening, while high-grade murmurs can sometimes be benign. Further testing will be necessary to determine the significance of your dog’s heart murmur.

Symptoms of Heart Murmurs in Dogs

Tired dog looking out window

A heart murmur is not a condition in and of itself, but rather a symptom of an underlying disease or defect affecting the heart. Many dogs with heart murmurs have no other symptoms, and they are sometimes discovered during routine physical exams. 

When dogs with heart murmurs develop symptoms, it is usually due to the progression of the underlying disease. 

Dogs with illnesses affecting the heart may show symptoms such as:

  • Coughing
  • Exercise intolerance
  • Weakness
  • Difficulty breathing
  • Lethargy
  • Collapse

What Causes Heart Murmurs in Dogs?

A heart murmur is caused by abnormally turbulent blood flow through the heart. Some heart murmurs can occur in healthy dogs or puppies and do not cause any problems. These are commonly known as “innocent” or “physiologic” murmurs. In puppies, an innocent murmur may resolve on its own as the puppy grows.

More commonly, a heart murmur is caused by an underlying illness or structural defect in the heart. Some structural causes of heart murmurs are congenital, meaning that the dog was born with a structural defect in the heart. 

Other types of heart disease leading to a murmur may be acquired or develop as a dog ages. These include conditions such as dilated cardiomyopathy (DCM) and myxomatous mitral valve disease (MMVD). These conditions can occur in any dog, but some breeds—including Boston Terriers, Cavalier King Charles Spaniels, Chihuahuas—are genetically predisposed to them.

In some cases, a heart murmur may be caused by factors outside the heart. For example, dogs on poor quality diets may develop nutritional cardiomyopathy due to a deficiency of certain nutrients. Other systemic conditions such as anemia or severe infections can also cause a heart murmur in dogs.

Diagnosing Your Dog With a Heart Murmur

Veterinarian taking dog blood work

Most heart murmurs are diagnosed by auscultation, which is when your veterinarian listens to your dog’s chest with a stethoscope. However, in most cases, additional diagnostic testing will be needed to determine the underlying cause of the murmur. 

Your veterinarian may recommend some or all of the following tests to help evaluate your dog’s heart:

Blood Work. A complete blood count and biochemistry panel will be performed to look for conditions such as anemia, infection, and hypoproteinemia, which may cause heart murmurs. Blood work also allows your veterinarian to determine whether other organ systems have been affected by the changes in the heart.

Radiography. Your veterinarian may recommend taking X-rays of your dog’s chest to evaluate the size, shape, and structure of your dog’s heart. Other organ systems that can be affected by heart disease, such as the lungs and the liver, can also be examined on an X-ray.

Echocardiography. An echocardiogram or “echo” is an ultrasound of your dog’s heart. This allows your veterinarian to visualize the structures of your dog’s heart, such as the chambers and valves. The movement of blood through the heart is also examined. An echo is usually the diagnostic test of choice for determining the severity and significance of your dog’s heart murmur.

Electrocardiogram. An electrocardiogram—also known as an EKG or ECG—measures the electrical activity of the heart and plots this activity on a graph. This test can help identify abnormal heart rhythms and enlargement of the heart which may be associated with a heart murmur.

Heart Murmur Treatment for Dogs

Man hugging dog

Because a heart murmur is usually a symptom of underlying heart disease, veterinarians typically do not treat the murmur itself. Instead, treatment is directed at correcting or managing the underlying disease. 

Depending on the disease, treatment may involve medication, surgery, or a combination of the two. 

If the disease is mild and your dog has no other symptoms, your veterinarian may even recommend postponing treatment and continuing to monitor the heart murmur until the disease progresses.

Medications for Dog Heart Murmurs

Treatment of heart conditions in dogs typically involves a combination of several medications to improve heart function and manage symptoms. Commonly used medications include:

Diuretics. Diuretics, such as furosemide, are sometimes referred to as water pills because they help remove excess fluid from the body. Diuretics are particularly important in dogs with congestive heart failure.

ACE Inhibitors. ACE inhibitors dilate blood vessels, lowering the blood pressure and reducing the workload on a dog’s heart. These are typically used in dogs with congestive heart failure.

Beta-Blockers. Beta-blockers, such as atenolol, may be used to slow the heart rate and reduce the oxygen demand of the heart. In some cases, they may also be used to regulate abnormal heart rhythms.

Calcium Channel Blockers. Calcium channel blockers are often prescribed for dogs with abnormal heart rhythms. They may also be used to slow the heartbeat and cause relaxation of the heart muscle.

Pimobendan. Pimobendan is a veterinary-specific drug that is used to help a dog’s heart pump more effectively. In some cases, it may slow the progression of heart disease and delay the onset of congestive heart failure.

Some cases of heart disease may also be treated with dietary management. Patients with congestive heart failure may be put on a special low-sodium diet to reduce fluid accumulation. 

If your dog’s heart disease was caused by a nutritional deficiency, a change in diet or the addition of supplements such as taurine may be recommended.

General Cost to Treat Heart Murmurs in Dogs

The cost to treat heart disease in dogs varies widely depending on the type and severity of the disease. Conditions that can be managed with medication alone may cost approximately $100-$800.

On the other hand, some heart conditions, such as congenital defects may require surgery. Cardiac surgery is highly invasive and often requires specialized care. Pet owners pursuing surgery should expect to spend several thousand dollars on treatment.

How to Prevent Heart Murmurs in Dogs

Most causes of heart murmurs cannot be prevented. However, just like in humans, factors such as obesity, poor diet, and lack of exercise can increase a dog’s risk of developing heart disease. 

Keeping your dog on a high-quality, commercially prepared diet and controlling portions to maintain a healthy, lean body weight can help reduce your dog’s risk of developing heart disease and many other illnesses later in life.

Related Conditions

  • Congestive Heart Failure
  • Dilated Cardiomyopathy
  • Pulmonic Stenosis
  • Mitral Regurgitation
  • Tricuspid Regurgitation
  • Anemia
  • Taurine Deficiency

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