Heart Murmurs in Cats

With an estimated 15 percent of cats affected by heart disease, early detection is essential. Heart murmurs may be one sign that something is amiss, which is why keeping regular veterinary appointments is so important. 

Not all cat heart murmurs signal heart disease and some are completely benign. To complicate matters, a cat can have heart disease without having murmurs. 

Consult this guide to learn what heart murmurs in cats are, how they’re diagnosed and treated, and how you can help protect your feline’s heart health.

What is a Heart Murmur?

Anything that changes how the blood flows through the heart’s chambers can cause a murmur. “If the valves in the heart chambers don’t open and close properly, blood will rush through and create an abnormal noise,” says Dr. Cathy Lund, owner of City Kitty Veterinary Care for Cats in Providence, Rhode Island. 

So instead of just the “thump thump” produced by a normal heartbeat, you’d hear an additional “whoosh” sound, says Dr. Sasha Gibbons, an associate veterinarian at Just Cats Veterinary Hospital in Stamford, Connecticut.

Cat Heart Murmur Grades

Veterinarians use a scale of one to six to evaluate the intensity (or loudness) of a heart murmur.

“A grade one is a very faint heart murmur that usually requires a quiet atmosphere to detect it. On the other side of the spectrum, a grade six heart murmur is so loud that it can be heard without a stethoscope,” explains Gibbons.

The volume of the murmur reflects the level of turbulence present in the heart, says Dr. Allison Bliss, veterinary staff and program manager for the ASPCA Kitten Nursery in New York City. The volume dictates the grade veterinarians give the murmur.

Grade 1 & 2	These murmurs are considered soft.
Grade 3	Heart murmurs at a grade three are considered moderately loud.
Grade 4	This grade is categorized as loud by veterinarians.
Grade 5 & 6	This level of murmur is what veterinarians refer to as palpable—meaning that it can be felt by placing a hand on the cat’s chest.

“In most cases, murmur intensity doesn’t correlate with the severity of the heart disease but a loud systolic murmur (higher than a grade four of six) is more worrisome for congenital heart disease in a kitten,” says Bliss.

Symptoms of Heart Murmurs in Cats

A cat heart murmur is not something you can effectively discover on your own. “Heart murmurs can only be detected by a veterinarian by using a stethoscope or through an echocardiogram, which is a specialized ultrasound of the heart,” says Bliss. 

You may, however, recognize symptoms related to the underlying cause, like heart disease.

Gibbons explains that some symptoms of heart disease in cats, that may or may not be present with a murmur, include:

• Elevated respiratory rate
• Panting
• Open-mouth breathing
• Coughing
• Exercise intolerance 

Sometimes though, cats with heart murmurs or heart disease may not exhibit any symptoms. “Many cats show no symptoms of heart disease,” says Gibbons. 

What Causes Heart Murmurs in Cats?

A heart murmur can indicate a disease of the heart muscle called cardiomyopathy, which is the most commonly acquired heart disease in cats, says Bliss. 

“Studies suggest that 30 to 50 percent of cats with a murmur have structural heart disease (1),” she says. “With structural heart disease, there is some sort of abnormal structure or defect that is disturbing the flow of blood, creating turbulence.” 

Structural heart disease can be either inherited or acquired. “Hypertrophic cardiomyopathy (HCM) in the Maine Coon and Ragdoll breeds is caused by two different genetic mutations,” adds Bliss.

Although heart murmurs typically occur as a result of an underlying heart condition, they can sometimes have other causes, says Bliss. Some of these include:

• Anemia
• Hyperthyroidism
• Heartworm disease
• Infection

Some murmurs—referred to as “innocent” murmurs—have no effect on the cat’s health. “They are often found in young kittens as they are growing and tend to go away with time,” says Bliss. “Older cats may develop one of these murmurs during high stress, but they are not an issue and won’t cause further complications.”

Diagnosing a Cat with a Heart Murmur

To diagnose a heart murmur, your veterinarian will listen to your cat’s heart with a stethoscope, says Gibbons. 

“If a heart murmur is detected, the veterinarian might recommend additional testing, such as bloodwork, x-rays, and blood pressure testing to determine the cause.” 

One of these blood tests is called proBNP, which Lund says can screen cats for abnormal heart muscle activity. “If this test is positive, it generally means that the murmur is the result of heart disease and not just from a fast heart rate.” 

The best way to evaluate heart function is with an ultrasound of the heart (an echocardiogram), says Gibbons. “An ultrasound looks at blood flow through the heart, how the valves are moving, and how the muscles in the heart are pumping to determine exactly what is causing the heart murmur.”

Heart Murmur Treatment for Cats

Cat heart murmur treatment depends on the diagnosis. “The treatment plan will typically be in line with how serious the condition is and may include diet changes, medications, and supportive care,” says Bliss. “The long-term treatment plan and prognosis depends on the severity of the heart condition.”

Some murmurs, like those caused by stress, are benign and require no treatment, says Gibbons. “Cats may be placed on medication to address anemia or infection if that is the cause of the heart murmur,” she adds.

Treatment for heart disease varies by the type. For example, with most cardiomyopathies, the heart becomes thickened or muscle-bound, says Lund. “The goal of treatment is to slow the heart down so the blood has time to get to where it needs to go.”

Depending on the type of heart disease present, veterinarians may use any of the following medications.  

• Anti-coagulants like Plavix, which thin the blood to prevent clotting
• Ace-inhibitors like Enalapril and beta blockers like Atenolol to slow the heart
• Medications like Pimobendin to help strengthen the heart and help it pump more efficiently
• Diuretics like Lasix, to help prevent fluid from accumulating

Cost to Treat Heart Disease in Cats

Heart disease can be expensive to treat, says Gibbons. “In Fairfield County, Connecticut, echocardiograms usually run between $350 to up to $950 depending on the qualifications of the sonographer.” 

Many heart medications are relatively inexpensive and can cost just a few dollars a month, she says. “But some can be up to a few dollars per pill.”  

Treatment costs for heart-related disease including murmurs will vary by location and veterinary clinic. 

How to Prevent Heart Murmurs in Cats

Cat heart murmurs generally can’t be prevented, says Bliss. “However, if one is detected during a routine appointment it is important to follow your veterinarian’s recommendations for follow up.” 

If your veterinarian detects a heart murmur, Bliss recommends yearly appointments to assess the heart and additional testing such as radiographs, bloodwork, and echocardiogram.

About 30 to 40 percent of cats with significant heart disease have no murmurs at all, says Lund, “So getting veterinary care and attention is enormously important to identify high-risk individuals.”

While the majority of heart disease is caused by genetic predisposition, it can occur with some nutritional deficiencies, says Gibbons, “which is why it is imperative to feed a commercial diet or review any home cooked regiments with a veterinarian or animal nutritionist.” 

While a heart murmur may or may not indicate heart disease, some afflicted cats have no murmurs. The most important takeaway is to bring your cat in for regular veterinary examinations to rule out disease and to begin a treatment protocol if needed.

Related Conditions

• Blood Clots
• Congestive Heart Failure 
• Arrhythmia
• Aortic Thromboembolism (Saddle Thrombus)
• Breathing Difficulties