No pet parent wants to hear that their dog's heart has a murmur, but it’s important to know what this means and how to move forward. A heart murmur in dogs is an abnormal sound heard during the heartbeat cycle, which may indicate an underlying problem with your dog’s cardiovascular system. It is important for dog owners to understand the causes and what to do next so they can make informed decisions about their pup’s care. In this article, we will discuss the causes of heart murmurs, the grading system, and diagnostic steps for dogs with a heart murmur.

What is a heart murmur in dogs?

A heart murmur in dogs is an abnormal heart sound heard with a stethoscope during the heartbeat cycle, which typically indicates a turbulent flow of blood in the heart or its surrounding vessels.

The sound of a heart murmur in dogs can vary in intensity and duration, ranging from a soft, barely audible noise to a loud, distinct sound. It is important to note that heart murmurs are not diseases themselves but rather a possibility of underlying cardiac issues.

Veterinarians will classify the heart murmur based on duration, intensity, and point (location) of maximum intensity. Based on this information, the heart murmur grade, known as heart murmur grades, can be determined.

What causes heart murmurs in dogs? Turbulent blood flow explained

A heart murmur in dogs may be due to physiological or pathological causes. Physiological or innocent murmurs typically occur in dogs less than 6 months of age (i.e. puppy murmur) and are not a reflection of a specific heart defect or disease. Innocent puppy or kitten murmurs often resolve by 5-6 months of age.

Other causes of a physiological heart murmur can include anemia, hypertension (high blood pressure), and fever, and may occur in very athletic dogs. Heart murmurs are often caused by turbulent blood flows within the heart or its surrounding vessels.

With pathological causes of a heart murmur in dogs, they are typically classified as either congenital (present at birth) or acquired (developing later in life). Congenital heart disease, present at birth, is a common cause of heart murmurs in young dogs.

Examples of congenital heart diseases that cause heart murmurs in dogs include issues with the aortic valve, such as aortic stenosis:

Other congenital conditions include ventricular septal defects, which create abnormal openings between the heart's chambers. These murmurs are typically high-grade and are present from a young age. Further investigation is highly recommended. Conditions affecting the mitral valve can lead to blood leaking back into the left atrium, contributing to heart murmurs.

Examples of acquired heart diseases that cause heart murmurs in dogs include:

  • Valvular insufficiency such as (MVD)
  • Dilated cardiomyopathy (DCM)
  • Infectious endocarditis
  • Heartworm disease

Chronic valve disease, particularly affecting the mitral valve, is a common cause of acquired heart murmurs in older dogs. These murmurs are typically high-grade as well but usually affect middle-aged or older dogs. Examples of acquired heart diseases that cause heart murmurs in dogs include a disease called dilated cardiomyopathy, which weakens the heart muscle. Dilated cardiomyopathy often affects the left ventricle, reducing its ability to pump blood effectively.

Types of heart murmurs in dogs

Heart murmurs in dogs can be classified into different types based on their timing, location, and characteristics. Understanding the type of heart murmur your dog has is important in determining the underlying cause and developing an effective treatment plan.

  • Systolic murmurs: These murmurs occur when the heart muscle contracts and are the most common type of murmur in dogs. Systolic murmurs are often associated with turbulent blood flow as the heart pumps blood out to the body.
  • Diastolic murmurs: These murmurs occur when the heart muscle is relaxed between heartbeats and are less common in dogs. Diastolic murmurs may indicate issues with the heart valves that prevent proper blood flow during the relaxation phase of the heartbeat.
  • Continuous murmurs: These murmurs occur throughout the heartbeat cycle and are often caused by conditions such as patent ductus arteriosus, atrial septal defect, or ventricular septal defect. Continuous murmurs are typically associated with congenital heart diseases that affect the normal flow of blood through the heart and its vessels.
  • Innocent murmurs: Innocent heart murmurs are mild are often found in puppies and do not signify an underlying heart disease. They can be caused by changes in blood flow or increased heart rate during exercise or excitement.

What are the grades of heart murmurs in dogs?

The grading system for heart murmurs in dogs is a crucial tool that helps veterinarians assess the severity and potential impact of the condition on a dog's cardiovascular health. This system consists of six grades, with Grade 1 being the mildest and Grade 6 being the most severe.

Grade 1: A Grade 1 heart murmur is characterized by a very soft, faint sound that may not be present during every heartbeat. These murmurs can be challenging to detect even for experienced veterinarians and often do not require any specific treatment.

Grade 2: Slightly louder than Grade 1 murmurs, Grade 2 murmurs are still relatively quiet and localized. They can typically be heard on one side of the chest but may not necessarily indicate a severe underlying issue.

Grade 3: A Grade 3 heart murmur is moderately loud and can be heard on both sides of the chest. These murmurs warrant further investigation to identify their cause and evaluate the need for treatment.

Grade 4: Loud and easily heard on both sides of the chest, Grade 4 murmurs are more likely to be associated with a significant underlying heart condition. At this stage, further diagnostic testing and potential intervention are necessary.

Grade 5: A Grade 5 heart murmur is very loud and can be heard even when the stethoscope is not in full contact with the chest. This grade is accompanied by a palpable vibration, known as a "thrill," indicative of a potentially severe heart issue that necessitates further diagnostic testing and possible intervention.

Grade 6: The most severe grade, Grade 6, is an extremely loud murmur and can be heard without a stethoscope touching the chest. This grade suggests a critical underlying heart condition that typically requires immediate and aggressive treatment to manage and alleviate its effects on the dog's overall health.

It is essential to recognize that the grade of a heart murmur in dogs is not always directly proportional to the severity of the underlying medical condition.

Your dog has a heart murmur, what should you do next?

What to do next often depends on many factors and the following questions should be considered when developing a plan.

In some cases, heart murmurs can progress and cause the dog to develop congestive heart failure.

Is the dog showing any symptoms of heart disease such as coughing, difficulty breathing, or exercise intolerance? If so, further diagnostic tests may be necessary to determine the underlying cause of the murmur.

Heart muscle disease, such as dilated cardiomyopathy, can also be a cause of heart murmurs in dogs.

What is the grade of the murmur? Murmurs are graded on a scale of 1 to 6, with 1 being very mild and 6 being very severe. The grade of the murmur can help determine the likelihood of it being associated with significant heart disease.

What grade of heart murmur is present?

While louder and higher-grade murmurs frequently indicate a more severe issue, it's not always the case; some lower-grade murmurs can also signify serious conditions. Most veterinarians will recommend further testing when the murmur is a grade 3 or above.

How old is your dog?

In dogs below the age of 3-4 years, congenital diseases are more prevalent, whereas acquired diseases tend to be less common in this age group. A grade 3 or higher murmur in a younger dog should always be investigated.

Are there any other clinical signs present?

Manifestations such as an elevated respiratory rate, increased respiratory effort, exercise intolerance, lethargy, and episodes of syncope (collapse) may arise due to compromised cardiovascular function stemming from heart disease. The presence of these clinical signs suggests a higher likelihood that the detected heart murmur indicates significant underlying pathology.

Diagnostic tests for evaluating heart murmur in dogs

Typically, echocardiography, including Doppler echocardiography, serves as the primary diagnostic tool for investigating heart murmurs in dogs. While this method is often sufficient for reaching a diagnosis, additional tests may be necessary to ascertain the severity and impact of the patient's condition.

Your veterinarian may recommend chest X-rays as the initial test as they can provide further information regarding the heart's size, shape, and position as well as identify signs of congestive heart failure or pulmonary edema. Chest X-rays can be performed easily at your veterinarian's office, whereas an echocardiogram often requires a referral appointment or having the specialist come to your animal hospital.

vet listening with a stethoscope

Your veterinarian may also recommend a blood test called NT-proBNP. This test measures the level of a protein in the bloodstream that is released from damaged heart muscle and can be used as an indicator of cardiac disease. the NT-proBNP test should be used in conjunction with other tests and not relied on solely to arrive at a diagnosis.

Prognosis for dogs with heart murmurs

The prognosis and outlook for dogs with heart murmurs depend on the underlying cause and severity of the condition. In some cases, heart murmurs can be a sign of a serious underlying condition, while in others, they may be harmless.

  • Innocent Murmurs: Puppies with innocent murmurs usually have a good prognosis and may outgrow the murmur as they mature. These murmurs are often benign and do not require any specific treatment.
  • Mild Heart Disease: Dogs with mild heart disease may have a good prognosis with proper treatment and management. Medications and lifestyle adjustments can help manage symptoms and improve the dog’s quality of life.
  • Severe Heart Disease: Dogs with severe heart disease may have a poor prognosis and may require aggressive treatment and management to manage symptoms and slow disease progression. Conditions such as degenerative mitral valve disease or dilated cardiomyopathy can lead to significant health challenges and may require ongoing veterinary care.

Monitoring and follow-up care for dogs with heart murmurs

Regular monitoring and follow-up care are crucial in managing heart murmurs in dogs. Your veterinarian may recommend regular check-ups, echocardiograms, and other diagnostic tests to monitor the progression of the condition.

  • Regular Check-ups: Regular check-ups with your veterinarian are essential in monitoring the progression of the condition and adjusting treatment plans as needed. These visits allow for early detection of any changes in your dog’s heart health.
  • Echocardiograms: Echocardiograms are a non-invasive test that uses ultrasound waves to visualize the heart and its structures. They can help monitor the progression of the condition and detect any changes in the heart. This test is particularly useful in assessing the function of the heart valves and the overall health of the heart muscle.
  • Other Diagnostic Tests: Other diagnostic tests such as X-rays, electrocardiograms, and blood tests may be recommended to monitor the progression of the condition and detect any changes in the heart. These tests provide additional information about the size, shape, and function of the heart, as well as the presence of any secondary conditions such as congestive heart failure.

By following your veterinarian’s recommendations for monitoring and follow-up care, you can help ensure that your dog receives the best possible care for their heart murmur. Regular check-ups and diagnostic tests are key to managing the condition and maintaining your dog’s overall health and well-being.

FAQs

What is the treatment for heart murmur in dogs?

As a heart murmur is not a disease, it is important to determine the cause of the murmur in order to develop an effective treatment plan. Depending on the underlying issue, treatment will typically involve medications to help.

Are heart murmurs in dogs serious?

The severity of a heart murmur will depend on its grade and the underlying condition causing it. Some lower-grade murmurs can be benign and may not require any treatment, while higher-grade murmurs can indicate serious underlying pathology. It is important to have your veterinarian evaluate the murmur to decide on the best course of action.

When should you worry about a heart murmur in your dog?

The combination of having a higher-grade heart murmur with clinical signs such as changes in breathing patterns, coughing, lethargy, and/or exercise intolerance would be a cause for concern. If your dog is displaying any of these symptoms, you should consult with your veterinarian as soon as possible. Furthermore, a heart murmur that increases in grades with time may also be a cause for concern.

In conclusion, a heart murmur in dogs is a relatively common finding and can result from various causes, including congenital heart defects, acquired heart diseases, and other factors. Identifying the cause and severity of a heart murmur is essential for determining the appropriate course of action. Diagnostic tests, such as echocardiography, chest X-rays, and blood tests, play an important role in evaluating a dog's heart health and uncovering the underlying issue.