My Cat Has a Heart Murmur - Causes, Symptoms and Treatment

A heart murmur is caused by turbulent flow of blood across a heart valve within the organ or from one of the large blood vessels exiting the heart. This flow causes an abnormal noise which can be detected via cardiac auscultation using a stethoscope. The heart makes various normal sounds which indicate proper organ functioning, but a murmur can interfere with these sounds.

During a normal cat heartbeat, we should be able to detect sounds such as the S1 ‘lub’ sound, caused by the opening of the aortic and pulmonary valves and closing of the atrioventricular valves. We can also hear the S2 ‘dub’ sounds which is the opening and closing of both the aortic and pulmonary valves. A heart murmur in cats can obscure these sounds.

Types of heart murmurs in cats

Heart murmurs can be systolic (during ventricular contraction) or diastolic (during ventricular relaxation). However, they can also be categorized due to their intensity. For this reason, there is an incremental grading system of feline heart murmurs which is used to chart the extent of the condition:

• Grade I: audible in a certain area and somewhat difficult to hear.
• Grade II: quickly detected, but quieter than normal heart sounds.
• Grade III: immediately audible at the same intensity as normal heart sounds.
• Grade IV: immediately audibly louder than heart sounds.
• Grade V: easily audible even when only approaching the chest wall.
• Grade VI: very audible, even with the stethoscope is away from the chest wall.

The degree of the murmur is not always related to the severity of the heart disease, since some serious pathologies of the heart do not produce any type of murmur. However, if the heart murmur can be heard even without a stethoscope, it implies there is a serious problem.

Veterinarians can also consider other factors when registering a heart murmur in cats. For example, the timing of the sound, the location within the heart and even the pitch. For this reason, it is important a trained veterinary professional examines the cat to know what they are looking for.

There are various medical conditions and disorders which can result in a cat having a heart murmur. Many of them are related to congenital issues, but there are other non-inherited causes. Generally, heart murmurs in cats are caused by:

• Anemia
• Lymphoma
• Congenital heart disease (e.g. ventricular septum defect, patent ductus arteriosus or pulmonary stenosis)
• Primary cardiomyopathy (e.g. hypertrophic cardiomyopathy)
• Secondary cardiomyopathy (e.g. hyperthyroidism or hypertension)
• Dirofilariasis or heartworm disease
• Myocarditis
• Endomyocarditis

As you can see, some parasitic diseases can affect the integrity of the cat's heart and lead to a heart murmur. Since a heart murmur is a symptom of another health problem, it can be secondary symptom of an underlying disease.

Learn more about some of these related conditions with our article on heart failure in cats.

You may also wonder if a heart murmur in an older cat is more likely. Senior cats are more likely to develop heart disease, but congenital heart murmurs can affect cats of all ages. Some young kittens may have a slight heart murmur which is usually detected around the time of the weaning period for cats. This can disappear before they reach maturity, but it is important to monitor the heart and diagnose any related conditions.

These types of heart murmurs are types of innocent or physiologic heart murmurs, sometimes known as non-athological heart murmurs^[1]. Other types of physiologic heart murmurs are related to stress. When a cat is feeling stressed for a certain reason, their heart rate may increase and they develop an innocent heart murmur. Once they cease being stressed, the heart rate should return to normal and the murmur disappears.

This can be difficult to detect in veterinary surgeries since the fact of being in at the clinic can cause the cat stress. Innocent or physiologic heart murmurs in cats are usually low grade, so the veterinarian should be able to distinguish them from more serious heart conditions.

The diagnosis of a feline heart murmur is made via cardiac auscultation, i.e. listening to the internal sounds of a body using a stethoscope. This is placed over the cat's thorax where the heart is located. The ‘gallop rhythm’ is a common sound of an abnormal heart beat, so-called due to the similarity of a galloping horse's footfall.

In addition to heart murmurs, the gallop rhythm is associated with various heart diseases and needs to be investigated thoroughly. If the cat has any ascites in the thorax, a full evaluation will be carried out after any pleural effusion or similar fluid build up has been drained.

In cases of a heart murmur, tests need to be carried out to determine if cardiac or extracardiac disease is at fault. For this reason, the following diagnostic tests will be carried out:

• Chest X-rays to evaluate the heart, its blood vessels and the lungs.
• Echocardiography or ultrasound of the heart to assess the state of the heart chambers (atria and ventricles), the thickness of the heart wall and the velocity of blood flow.
• Biomarkers of heart disease such as troponins or pro-brain natriuretic peptide (Pro-BNP) in cats with signs suggestive of hypertrophic cardiomyopathy. This is when an echocardiography cannot be performed.
• Blood and biochemical tests with measurement of total thyroxine hormone Free T4 for the diagnosis of feline hyperthyroidism, especially in cats older than 7 years.
• Tests for the detection of heartworm parasitism.
• Tests to detect infectious diseases, such as Toxoplasma and Bordetella serology and blood culture.
• Measurement of high blood pressure.
• Electrocardiogram looking for arrhythmias.

Is there a test to determine the risk of hypertrophic cardiomyopathy?

If the feline is going to reproduce or if they are a certain breed, it is best to carry out genetic tests for hypertrophic cardiomyopathy. This is because it is best to avoid perpetuating the genetic mutation. Breeds commonly affected by this gene include the Maine Coon, Ragdoll and Siberian cats.

However, even if the parents test positive for the gene, it doesn't necessarily mean they will develop the disease. It simply indicates they are at a greater risk. As a likely consequence of unidentified mutations, it is possible a cat which tests negative can still develop hypertrophic cardiomyopathy. If you have a cat which is predisposed to this disease, you should ideally carry out annual echocardiography tests. Generally, sterilization is recommended to prevent propagating the gene.

If the diseases are cardiac, such as hypertrophic cardiomyopathy, medications for the correct function of the heart will be prescribed. These also help to control the symptoms of heart failure in cats. Treatment will depend on the underlying cause and can include:

• Drugs for hypertrophic cardiomyopathy can include myocardial relaxants such as the calcium channel blocker diltiazem, beta blockers such as propranolol or atenolol, or anticoagulants such as clopidogrel. In cases of heart failure, the sequence of treatment will likely start with diuretics, vasodilators, digitalis and other heart medications.
• Hyperthyroidism can cause a problem very similar to hypertrophic cardiomyopathy, so the disease must be controlled with drugs such as carbimazole or methimazole for cats. Some cases may require effective therapies such as radiation therapy.
• Hypertension can cause left ventricular hypertrophy and congestive heart failure, although it is more infrequent. It generally does not require treatment if the increase in blood pressure is treated with drugs such as amlodipine.
• Although it is rare in cats, if they have myocarditis or endomyocarditis the treatment will require antibiotics.
• In heart disease caused by parasites such as heartworm or toxoplasmosis, specific treatment must be carried out against these diseases.
• In cases of congenital diseases, surgery is usually the indicated treatment.

Since the treatment of the murmur in the cat's largely heart depends on the cause, it is important to visit the veterinarian to carry out the appropriate tests and determine the drugs to be taken. This will also likely include information on how to manage symptoms.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to My Cat Has a Heart Murmur - Causes, Symptoms and Treatment, we recommend you visit our Cardiovascular diseases category.