Heart Murmurs in Dogs and Cats

Laurie Anne Walden, DVM

Photo by Tracy Anderson on Unsplash

A heart murmur is an abnormal whooshing heart sound. A heart murmur isn’t a diagnosis of heart disease; it’s a clinical sign showing that something has made blood flow within the heart turbulent. Some of the things that cause heart murmurs are benign and don’t need treatment. Others are serious conditions that can lead to heart disease and heart failure.
 
Causes
Anything that alters the flow of blood inside the heart can cause a murmur. Leaky heart valves (flaps that control blood flow between heart chambers) and disorders of the heart muscle are the most common causes of murmurs in adult dogs and cats. Examples are mitral valve degeneration, usually in older dogs or inherited in Cavalier King Charles spaniels, and hypertrophic cardiomyopathy in cats. Anemia—“thin” blood with a low red blood cell count—can also cause a murmur because of the change in blood consistency.
 
Young puppies and kittens sometimes have congenital heart murmurs, which are murmurs present from birth. These murmurs are usually benign and disappear on their own as the animal grows. However, some congenital murmurs are caused by structural defects of the heart or the large blood vessels around the heart, and these defects can have severe consequences if they aren’t (or can’t be) repaired.
 
Signs
Heart murmurs are usually heard for the first time during routine wellness examinations in animals with no signs of heart problems. Early diagnosis and treatment improves the prognosis for animals with heart disease, so listening to the heart with a stethoscope is a crucial part of the annual examination.
 
Heart murmurs are graded according to their loudness, ranging from barely audible to so loud they can actually be felt with a hand placed on the rib cage. The loudness of a murmur doesn’t necessarily correspond to the severity of the condition that caused it (serious conditions can cause quiet murmurs).
 
These are some signs of heart disease and heart failure:

• Coughing
• Labored breathing
• Lack of energy
• Swollen belly
• Blue or purple gums
• Fainting or collapse

 
Diagnosis
The best way to identify the source of a heart murmur is with an echocardiogram, an ultrasound study of the heart. An echocardiogram, usually performed by a veterinary cardiologist, shows the shape of the heart valves, thickness of the heart muscle, blood flow within the heart, and measures of heart function.
 
Chest radiographs (x-ray images) can be used to diagnose heart disease once the disease has progressed to the point of changing the size and shape of the heart chambers. A blood test that can be used to screen for heart disease is the concentration of NT-proBNP (N-terminal pro–brain natriuretic peptide), a substance released by heart muscle cells in response to excessive stretch and strain.
 
If your pet has a heart murmur, start monitoring the sleeping respiratory rate. An increased sleeping respiratory rate can be a sign of heart disease. Wait until your pet is asleep, count the number of breaths (each rise of the chest) in 15 seconds, and multiply by 4 to calculate the number of breaths per minute. A sleeping rate of more than 35 breaths per minute or a rate that’s increasing over time warrants a visit to your veterinarian.
 
Treatment
Treatment depends on the cause of the heart murmur and whether the animal has heart disease. Heart disease is treated with medications and possibly prescription diets. Dogs and cats don’t get coronary artery disease (plaque in the arteries) like humans do, so the treatments and dietary recommendations are not the same for animals as they are for humans with heart disease. All animals with murmurs, whether the cause is serious or thought to be benign, need regular monitoring (sleeping respiratory rate, veterinary examinations, and possibly follow-up echocardiography) so changes in heart function can be identified and treated promptly.
 
Image source: https://unsplash.com/photos/a-brown-and-white-dog-sitting-on-top-of-a-wooden-floor-OktYfwY5ZQI

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