How bad is a Grade 4 heart murmur in dogs? Here’s the Answer

Mild chronic valve disease that leads to small leaks across the mitral valve usually does not create a problem for a dog. The disease is slowly progressive in most cases and the leak will continue to worsen over months to years. If the disease becomes severe, the dog is at risk for developing congestive heart failure. Congestive heart failure means that the leak across the heart valve overwhelms the heart and fluid goes from the heart backwards into the lungs (instead of from the heart forward to the body). Signs of congestive heart failure include cough (especially a cough at rest), a fast breathing rate (especially at rest), difficulty breathing, fainting, weakness, lethargy, exercise intolerance and/or abdominal distension.

A heart murmur is an abnormal heart sound that is heard when listening to the heart with a stethoscope. It is caused by abnormal turbulent blood flow. Abnormal turbulent blood flow can occur when blood passes across abnormal heart valves or across abnormal structures within the heart. It can also occur when blood flows very fast across normal structures (such as when an animal is excited). An echocardiogram (ultrasound of the heart) is a non-invasive test that is performed to determine the cause of the murmur.

Loud heart murmurs (Grade 3-4/6 to 6/6) in a new puppy or kitty and soft heart murmurs that persist beyond 14-16 weeks of age should be evaluated by a cardiologist. This may indicate that congenital (present at birth) heart disease is present. The cardiologist will perform an echocardiogram as well as other tests (EKG, blood pressure, etc.) to assess the heart and determine if congenital heart disease is present. Depending on the disease present, some congenital diseases can be fixed or made better with an interventional catheter procedure, traditional surgery, or administration of cardiac medications.

A cardiologist can perform an echocardiogram and determine if hypertrophic cardiomyopathy or other structural heart disease is present in susceptible breeds and in cats that have abnormal heart sounds on physical examination. The progression of disease is different in every cat. Some cats develop congestive heart failure soon after their disease is diagnosed by echocardiogram. Other cats remain asymptomatic for their hypertrophic cardiomyopathy for many years before they develop congestive heart failure. Still others never develop congestive heart failure or any symptoms of their heart disease. Recheck cardiology visits and echocardiograms are necessary to determine the progression of disease in each patient. If a cat develops clinical symptoms of congestive heart failure, X-rays are used to confirm the presence and determine the severity of the congestive heart failure. If congestive heart failure is present, oral medications can be prescribed to help maintain a good quality of life, and some cats can do well with these medications for a period of months to 1-2 years.

Heart murmurs in cats can be due to the excitement of the veterinary visit (physiologic heart murmurs) or due to underlying heart disease. An echocardiogram is necessary to differentiate between a heart murmur that is just due to excitement versus a heart murmur from underlying heart disease. Heart murmurs (or other abnormalities heard with a stethoscope) may indicate that cats have a disease called hypertrophic cardiomyopathy. This is the most common acquired heart disease seen in cats. Hypertrophic cardiomyopathy is a disease of the pumping chamber of the heart where the muscle does not relax well after it contracts. Blood is then unable to fill the heart normally and fluid goes from the heart backwards into the lungs (instead of from the heart forward to the body). This is known as congestive heart failure. Signs of congestive heart failure include a fast breathing rate, difficulty breathing, fainting, weakness, lethargy, hiding and a decreased appetite. Unfortunately, in addition, these cats can also pass away suddenly from abnormal heart beats from the diseased heart chambers. Some cats can develop signs of arterial thromboembolism, in which a clot forms within the heart, exits the heart, and interrupts blood flow to tissues/organs of the body (including the front or back legs).

Does a heart murmur mean my dog has heart disease?

Not necessarily; not all dogs diagnosed with a heart murmur will suffer from cardiac (heart) disease. A heart murmur is a clinical finding—not a disease diagnosis. Some heart murmurs are benign or harmless and may go away on their own, particularly in puppies.

The only way to know the significance of your pet’s murmur is to work with your veterinarian and/or a Veterinary Cardiologist (specialist) to determine the cause of the murmur and the severity of the heart disease, if present. Additional diagnostic testing, such as an echocardiogram (ultrasound of the heart) will likely be required.

What are treatment options for dogs with heart murmurs?

Treatment is designed to relieve the issues associated with heart disease related to the murmur. Some dogs with heart murmurs may live normal lives and never require treatment; others with more severe disease will benefit significantly from treatment, which can range from oral medications to surgery.

A veterinary cardiologist will tailor a treatment plan to improve your pet’s quality of life, as well as extend the time you have together. Depending on the cause of the murmur, treatment may sometimes “cure” the murmur. For example, if your dog is diagnosed with a patent ductus arteriosus (PDA), surgery can correct this abnormality, eliminate the heart murmur and a normal life expectancy is anticipated. This is why investigating the cause of a murmur with further testing by a veterinary cardiologist can be critical.

Heart Murmurs in Dogs

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It is scary when your dog has been diagnosed with a heart murmur. Heart murmurs affect around 60% of dogs over the age of 5 years old.

When your vet is listening to your dog’s heart through a stethoscope, they can hear the rhythmical lub-dub. This sound is made from the normal opening and closing of the heart valves (explained further later on). When there is any turbulence of blood flow, the lub-dub is replaced by a swoosh noise – swoosh-dub, swoosh-swoosh, etc. This is what we call a heart murmur.

It is important to know that a heart murmur is not a name for a disease, but a name for what we hear – and heart murmurs can be caused by many different conditions.

Not all heart murmurs sound the same. Some have different intensity, location and time. The intensity of the murmur does not usually correlate with the severity of heart disease. Veterinarians grade the intensity of the heart murmur into 6 different grades.

As noted, a heart murmur is caused by turbulence blood flow within the heart. A heart murmur can also be classified as an innocent/physiologic murmur. An innocent heart murmur has no impact on the dog’s health. This most often occurs in young puppies and they eventually outgrow the murmur by around 5 months of age. If your vet has detected an innocent heart murmur in your young puppy, your vet will most likely recommend listening to the heart again when your puppy is 4-5 months of age. If the heart murmur is still present, a cardiac work up will be warranted.

More commonly, heart murmurs in older dogs are caused by cardiac disease (pathological murmurs) or a problem outside the heart.

If your vet detects a heart murmur during your dog’s physical exam, certain tests may be recommended depending on the grading, location and time of murmur.

The first test that you vet may recommend to investigate your dog’s heart murmur is an echocardiogram. This is an ultrasound of the heart performed by a specialist. An echocardiogram is extremely valuable because it will give us a diagnosis of what is causing the heart murmur. It will also examine the health of the heart valves, measure the blood pressure to the lungs and examine any secondary changes to the heart including abnormal thickness.

A chest x-ray may also be recommended to look at the chest. A chest x-ray provides us valuable information about the chest cavity. This includes looking at the lungs to see if there is any fluid if the heart is putting any pressure on the windpipe and to measure how big the heart in the chest cavity.

There are NO signs if we detect the heart murmur early. Every year your vet will listen to your furbaby’s heart for any murmurs during their yearly health check ups.

Heart murmurs with pathological heart diseases usually progress into congestive heart failure. This is a serious condition and can be fatal. Commonly, dogs that are in heart failure will have an accumulation of fluids in their lungs. Dogs with heart failure may also have a cough, exercise intolerance or difficulty breathing.

Coughing can also be a sign of respiratory diseases such as bronchitis, allergies, pneumonia, asthma or kennel cough. Hence, it is very important for your vet to perform a thorough workup.

Treatment for your dog’s heart murmur will depend on the underlying cause. An innocent murmur will not require any treatment, but regular monitoring of your dog’s heart condition is recommended to ensure no other problems develop.

A heart murmur caused by cardiac disease may require medication(s) and a specialised diet. Your dog will need regular vet visit for a routine monitoring every 6 months. This may include a repeat echogram and/or x-rays depending on your dog’s conditions.

Your veterinarian will advise you on the best course to treat and monitor your dog’s heart murmur.

Your veterinarian will discuss the prognosis and treatment options for your dog as each case is specific and different. In all cases, ongoing monitoring and regular diagnostic testing are needed to monitor the heart murmur.

At My Vet Animal Hospital, we work closely with specialists in Small Animal Medicine and advanced training in Cardiology. We are able to organise a specialist to come to our clinic for an echocardiogram, rather than you travelling to a specialist hospital. We also offer diagnostic x-rays and blood testing in house for immediate results. If your dog needs special heart medication and doesn’t like tablets, we can also offer personalised compounded medicine with added flavour including chicken, beef or fish. This is our way to ensure your dog has an accurate course of diagnosis, access to gold-standard monitoring tests and the best treatment.

If you have any concerns about your dog’s heart, please do not hesitate to reach out to us!

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