Heart Murmur in Cats: What It Is and How to Manage

What is Heart Murmur in Cats?

A heart murmur is an abnormal heart sound noted when listening to your pet’s heart with a stethoscope. A heart murmur results from an underlying health condition, such as weak heart valves that triggers this abnormal sound.  

Typically, there are only two heart sounds that are considered normal. An extra heart sound or a “whooshing” noise heard when the heart beats is considered a heart murmur and is a common finding in middle aged to older cats. 

In some cases, it can be found in younger cats and can be a concern for congenital issues (those present at birth), but this is quite rare.   

The “whooshing” noise or heart murmur itself is caused by turbulent (rough) blood flow through the heart. Blood should flow through the four normal chambers of the heart and through the valves (doorways between chambers) in a smooth, calm way. When there are barriers to flow, turbulence occurs and it changes the normal “lub” and “dub” heart sounds.   

Turbulence can be caused by heart valve malfunctions, holes in the walls of the heart or arteries, or narrowing of blood vessels or heart chambers. Turbulence can also occur from excitation and fast heart rates or thinning of the blood (anemia).  

Heart murmurs are classified three ways:  

• Based on their grade (the loudness of the murmur)  

• Configuration (when the murmur is the loudest during contraction and relaxation of the heart)  

• Location of the murmur (when listening with a stethoscope)  

Veterinarians grade heart murmurs on a scale of 1–6 depending on how loud the heart murmur is upon listening. This is a subjective scale based on what the specific veterinarian hears while listening to the heart with a stethoscope. The grade for heart murmurs include: 

• Grade I: audible only to a trained ear or hardly heard at all  

• Grade II: soft but audible  

• Grade III: intermediate and the most common grade of heart murmur  

• Grade IV: louder murmur that radiates across the heart, often on both sides of the chest  

• Grade V: loud heart murmur with a noticeable “thrill” or vibration felt when touching the chest wall  

• Grade VI: loudest heart murmur heard before the stethoscope even touches the chest and often has a noticeable “thrill” or vibration felt when touching the chest wall  

Finding the location of the heart murmur is difficult in cats because of their small chest cavities, and it’s often heard best along the sternum.  

The grade, location, and configuration of heart murmurs is helpful for finding the underlying cause.   

Heart murmurs can be congenital or acquired. Congenital heart murmurs are present at birth or soon after birth and are often associated with heart defects. These types of murmurs can be quiet early in life and are not always found until later with growth and maturation.   

Acquired heart murmurs occur at any point in life and can be benign (no underlying disease causing the murmur) in cause or may be associated with heart disease (HCM in cats). 

Some heart murmurs are called “innocent” or benign. This means that there is no underlying heart disease causing the abnormal heart sounds. They are found often in cats of any age and are usually intermittent (sounds come and go) and are quiet when listened to with a stethoscope. 

Symptoms of Heart Murmur in Cats

Pet parents will typically not notice any symptoms in cats until heart disease progresses and signs of congestive heart failure or thromboembolism (blood clots) develop.  

Heart murmurs are usually found incidentally during a routine physical examination. Your veterinarian will discuss possible causes and next steps for diagnosis.    

Symptoms of severe heart disease, heart failure, and thromboembolism include:  

• Chronic weight loss or muscle wasting  

• Decreased appetite  

• Hiding behavior  

• Weakness  

• Coughing or wheezing  

• Exercise intolerance—panting with mild exertion  

• Increased respiratory rate at rest  

• Increased effort to breathe 

• Fluid from mouth or nostrils  

• Change in the color of the gums to blue, gray, or white  

• Lethargy  

• Collapse  

• Paralysis of the hind limbs  

• Painful vocalization  

• Stunted growth in kittens with severe congenital causes  

Causes of Heart Murmur in Cats

The cause of a heart murmur in a cat can be due to various underlying conditions such as:  

• Anemia  

• Anxiety 

• High blood pressure  

• Heart disease 

• Hypertrophic cardiomyopathy (HCM) 

• Heart wall defects or holes in the heart walls (atrial or ventricular septal defects)  

• Heart valve deficiencies: mitral, tricuspid, or aortic valves  

• Stenosis (narrowing) of the valves: subaortic, aortic, mitral, tricuspid, or pulmonic valves  

• Patent ductus arteriosus (PDA): a congenital heart defect where an important blood vessel fails to close properly following birth  

• Tetralogy of Fallot: severe congenital malformations of the heart  

• Thromboemboli (blood clots) in the heart or vessels  

• Heartworm disease  

• Endocarditis (infection of one or more heart valves)  

Maine Coons are prone to moderate to severe HCM and HOCM. Persian cats, American Shorthairs, and British Shorthairs are also prone to less severe cases of inherited HCM. Siamese cats have a higher rate of congenital PDA and inherited dilated cardiomyopathy (DCM). 

How Veterinarians Diagnose Heart Murmur in Cats

The cause of a heart murmur in a cat is typically not found by using a stethoscope alone to listen to the lungs, though this can be helpful in determining the location, configuration, and grade of the murmur.  

Unfortunately, a benign or innocent heart murmur can sound like a heart murmur caused by severe heart disease in a cat. So all heart murmurs will need to be evaluated thoroughly by a veterinarian to ensure the health of your cat. 

Your veterinarian will likely recommend full blood work, including a cardiac proBNP, which gives a quantifiable number value to the amount of stretch on the heart muscle itself. Concerning symptoms and consistently increased levels of proBNP can suggest underlying heart disease in cats.   

Blood work can help rule out anemia or underlying systemic disease, such as hyperthyroidism, which can contribute to heart disease.   

Chest radiographs are often recommended to assess the size of the heart, to evaluate the vessels going to and from the heart, and to assess the lungs for any signs of fluid or congestive heart failure (CHF).   

An echocardiogram or ultrasound of the heart is considered the gold standard to investigate the underlying cause of a heart murmur. Sometimes an electrocardiogram (EKG) is recommended if an abnormal heart rhythm is noted.  

Treatment of Heart Murmur in Cats

A heart murmur itself does not require treatment, but the underlying cause of the heart murmur may need to be addressed.  

Treatment depends on the underlying cause and severity of the heart murmur. Benign or innocent murmurs usually require no treatment at all. Often, cat age, overall health, and the cost of therapy are major considerations with treatment of heart disease in cats.  

CHF, depending on its severity, often requires hospitalization, diuretics (furosemide), cardiac medications (benazepril), and oxygen therapy. In many cases of CHF in cats, pleural effusion (fluid buildup around the lungs) needs to be removed by a procedure called thoracocentesis to allow the lungs to fully expand again.   

Some congenital heart murmurs, such as small holes in the heart walls (or septal defects), may resolve within six months as the animal grows. In some cases of congenital heart disease in cats, surgery is necessary to close a PDA or septal defect.   

Treatment of other underlying health conditions, such as anemia or hyperthyroidism, may help with underlying heart murmurs.  

Each case is different, so your veterinarian will work with you to determine the best diagnostic and treatment plan while also discussing the prognosis for your cat.  

Recovery and Management of Heart Murmur in Cats

Close monitoring of heart murmurs and heart disease is necessary to check for progression of the condition. Management of CHF and congenital cardiac issues in cats is done with regular veterinary checkups every few months, bloodwork, and X-rays to monitor whether the cat is stable or if medications need to be added or adjusted.  

Prognosis ranges from excellent when discussing benign heart murmurs to grave when discussing severe congenital or acquired heart disease.

Long-term prognosis varies depending on the underlying cause of the heart murmur and response to treatment. Focus is not placed on cure in most cases, rather it is placed on quality of life and comfort for your cat.