Heart Murmur In Dogs: Can They Outgrow It?

Heart murmurs in dogs are caused by turbulent blood flow within the heart. They can range from 'innocent' or 'physiologic' murmurs, which are usually harmless and often found in young puppies, to more severe pathologic or extracardiac murmurs, which are caused by heart disease or other health issues. Innocent heart murmurs are typically soft and quiet and will usually be outgrown by the time a puppy is 4-6 months old. However, if a puppy does not outgrow its murmur, further evaluation by a veterinarian is recommended to determine the cause, cardiac status, and prognosis. While innocent heart murmurs do not require treatment, it is important to monitor them through regular veterinary check-ups and echocardiograms to ensure they do not develop into something more serious.

What is a heart murmur?

A heart murmur is an abnormal heartbeat sound caused by turbulent blood flow within the heart. It is an additional whooshing noise caused by turbulence in the flow of blood as it passes through the heart. In other words, a heart murmur is a sound made by the blood flowing through the heart's valves.

When a veterinarian listens to a dog's heart through a stethoscope, they will be able to hear the regular sounds of the blood flowing through the heart's valves. If the sound is unusual or doesn't follow the regular pattern, it is called a heart murmur. A typical heartbeat makes two sounds like "lub-dub" when the heart valves are closing. A heart murmur may occur when the heart is filling with blood (diastolic murmur), when the heart is emptying (systolic murmur), or throughout the heartbeat (continuous murmur).

Heart murmurs can be present at birth (congenital) or develop later in life (acquired). Congenital murmurs are usually caused by a structural heart defect. Most murmurs in young puppies are benign, soft, and quiet and are called "innocent" or "physiologic" murmurs. These innocent heart murmurs are usually outgrown by about 5-6 months of age and do not require any treatment. However, if a puppy does not outgrow its murmur, an echocardiogram is recommended to determine the cause, cardiac status, and prognosis.

An acquired murmur is one that becomes apparent later in life. These are usually due to heart valve abnormalities or cardiac muscle disease. The most common cause is myxomatous mitral valve degeneration, which is a progressive degeneration of the mitral valve. The mitral valve is the valve between the left atrium (upper chamber) and left ventricle (lower chamber) of the heart. When the mitral valve degenerates, it becomes bumpy and irregular and does not close completely, allowing blood to flow backward. This condition is known as chronic valve disease, degenerative mitral valve disease, or endocardiosis.

What causes a heart murmur?

A heart murmur is caused by rapid, choppy, or turbulent blood flow through the heart. This can be caused by a number of factors, including:

Innocent or Physiologic Murmurs

Innocent heart murmurs are common in newborns and children and usually don't require treatment. They can be caused by:

• Lack of healthy red blood cells (anemia)
• Overactive thyroid (hyperthyroidism)
• Phases of rapid growth, such as adolescence
• Physical activity or exercise

In puppies, innocent heart murmurs can be caused by changes in blood flow or increased heart rate during exercise or excitement. They may also be caused by genetic factors or differences in heart anatomy.

Worrisome Murmurs

More serious heart murmurs are usually caused by problems with the heart's structure or function. These can include:

• Holes in the heart, such as atrial or ventricular septal defects
• Cardiac shunts, which cause irregular blood flow between the heart chambers or blood vessels
• Heart valve problems, such as mitral valve prolapse or aortic stenosis
• Endocarditis, an infection of the heart valves or lining
• Calcium buildup on the heart valves
• Tumors, such as carcinoid syndrome
• Marfan syndrome, an inherited condition affecting connective tissue
• Rheumatic fever, a complication of untreated strep throat

In larger dog breeds, heart murmurs are often caused by dilated cardiomyopathy, a disease that weakens the heart muscle. In small dogs, heart murmurs are commonly caused by a leaky mitral valve, also known as chronic valve disease or degenerative mitral valve disease.

What are the symptoms of a heart murmur?

The symptoms of a heart murmur depend on the underlying cause, and whether the murmur is considered 'innocent' or harmless, or a sign of a more serious heart condition.

Innocent heart murmurs usually don't cause any other symptoms. They are common in newborns and children, and can be caused by a lack of red blood cells, an overactive thyroid, phases of rapid growth, or physical activity. These murmurs may go away over time.

However, symptoms of a more serious heart murmur may include:

• Blue or gray fingernails or lips
• A persistent cough
• Heavy sweating with little or no activity
• Poor appetite and lack of growth (in infants)
• Sudden weight gain or swelling
• Shortness of breath during exercise or when sleeping
• Dizziness or fainting for no obvious reason
• Fast heartbeat (palpitations)
• Weakness or lethargy
• Exercise intolerance
• Collapsing or fainting
• Severe water retention
• Lack of energy or appetite

How can heart murmurs be treated?

Heart murmurs in dogs can be treated in several ways, depending on the underlying cause.

If the heart murmur is deemed 'innocent' or 'physiologic', meaning it is not a sign of heart disease, then it will likely not require any treatment. Innocent heart murmurs are usually found in young puppies and can be caused by factors such as changes in blood flow or increased heart rate during exercise or excitement. Puppies' hearts are still developing, and some breeds may even have a genetic predisposition to innocent heart murmurs due to differences in their heart anatomy. Innocent heart murmurs often disappear as the puppy matures, but if they persist or are accompanied by other symptoms, further evaluation and treatment may be necessary.

For heart murmurs caused by cardiac disease or defects, treatment options may include medication, a specialized diet, or surgery. Medications can help prolong a dog's life or improve their quality of life, especially in cases of a leaky mitral valve. A specialized diet, such as a cardiac prescription diet, can also help support cardiac health by managing weight and providing essential nutrients. In some cases, surgery may be an option to correct congenital heart defects.

Regular monitoring of the dog's heart is crucial, and this may include repeat echocardiograms and/or X-rays every 6 months or annually to track the progression of the murmur. Additionally, certain blood tests, such as the pro-BNP (precursor of B-type natriuretic peptide) test, can be useful monitoring tools as they can indicate cardiac muscle stretch and stress.

The prognosis for dogs with heart murmurs varies from good to severe, depending on the underlying cause. Innocent murmurs that don't require treatment typically have a good to excellent prognosis, while those caused by extracardiac disease or functional problems may resolve over time with proper management. For dogs with leaky mitral valves or dilated cardiomyopathy, the prognosis is more varied, with some dogs never developing congestive heart failure if they receive proper care.

What is the prognosis of a heart murmur?

The prognosis of a heart murmur in dogs varies from good to severe, depending on the underlying cause of the murmur.

Innocent murmurs, which are usually found in young puppies, are benign and do not require treatment. They are typically outgrown by the time the puppy is between four and six months old. In these cases, the prognosis is generally good to excellent.

Heart murmurs caused by extracardiac disease or a functional problem that can be treated may resolve over time. For dogs with a leaky mitral valve, long-term medication can help prolong their lives or improve their quality of life.

The prognosis for dogs with dilated cardiomyopathy varies. If the dog is already showing signs of heart failure, the prognosis is poor. For dogs with congenital heart defects, the prognosis also varies. If the defect can be corrected by surgery, the prognosis is usually very good.

The prognosis for a dog with bacterial endocarditis depends on the severity of the infection and the valve that is affected. Acquired murmurs vary significantly in their prognosis. A dog with mitral insufficiency can usually be managed with long-term medication.

The prognosis for a dog with a heart murmur caused by congenital heart disease is extremely variable, depending on the specific type of defect present. Overall, the prognosis ranges from excellent to grave, depending on the cause of the murmur.

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