Heart murmurs in dogs are abnormal sounds caused by turbulent blood flow through the heart. They can typically be heard through a stethoscope during veterinary exams. Although a heart murmur is not always a cause for concern, it can indicate other serious problems in the body, especially heart disease. Because heart disease can lead to serious health problems if left untreated, heart murmurs require veterinary attention to determine if other illnesses are present. Here’s what you need to know if your vet has diagnosed your dog with a heart murmur.
What is a heart murmur?
A heart murmur is an abnormal heart sound that resembles a hissing sound when listened to with a stethoscope. It occurs when there is turbulent blood flow in the heart.1 A heart murmur is not a disease in itself, but it can indicate heart disease or another problem in the body.
The heart consists of four chambers: the right atrium, the right ventricle, the left atrium and the left ventricle. In a normally functioning heart, deoxygenated blood flows from the veins into the right atrium and is pumped into the right ventricle. The blood flows through the pulmonary artery, becomes saturated with oxygen and enters the left atrium. This oxygen-rich blood is pumped through the left ventricle of the heart and enters the body via the arteries. Valves between each chamber and the blood vessels ensure that blood moves in the correct direction. Any disruption to the heart’s natural blood flow can cause turbulence, which can be heard with a stethoscope.
Heart murmur levels in dogs
Heart murmurs are typically graded by intensity on a scale of one to six (I-VI). Grade I heart murmurs are the mildest and can be difficult to detect. These noises are quiet and may occur intermittently. Grade VI murmurs are the most serious. These are very loud when listened to with a stethoscope and can usually be felt when the dog places his hands on his chest. The higher the degree of a heart murmur, the greater the turbulence in blood flow in the heart.
Symptoms of heart murmurs in dogs
Dogs with heart murmurs may or may not show clinical signs of illness. Your veterinarian may detect an incidental heart murmur when listening to your dog’s heart as part of a routine health exam, even if there are no symptoms.2 Because a heart murmur is a sign of a possible heart problem, but not an actual disease, the presence of other symptoms depends on it the degree of underlying disease, if any.
If your dog has a history of a heart murmur, watch for signs of serious problems such as heart failure or moderate symptoms that indicate a test should be done. The following symptoms may occur in dogs with heart disease, which may be indicated by a heart murmur.
Cough
Coughing is a common sign of heart disease. Swelling of the heart can cause pressure on the airways, and turbulent blood flow can also cause fluid to build up in the lungs. Both are common causes of coughing in dogs with heart disease.3
Lethargy, exercise intolerance or weakness
Exercise intolerance is another common sign of cardiovascular disease in dogs.3 Your dog may tire quickly during exercise or activities. They may appear weak or lethargic even at home due to inadequate heart function.
Unusual breathing or wheezing
Dogs with heart problems may breathe quickly, experience difficulty breathing, or pant more than usual. Difficulty breathing in dogs with heart disease can be particularly noticeable at night when sleeping or getting up from lying down.1
Heart murmurs in dogs. VCA Animal Clinics.
Pale gums
Pale gums are associated with more serious stages of heart disease in dogs, but can also be a sign of many other diseases. If you notice that your dog’s gums are a color other than pink, make an appointment with your veterinarian to determine the cause.
Distended stomach
Dogs with right-sided heart disease may experience abdominal distension, giving the impression that the abdomen is bloated. This is caused by fluid buildup in the abdomen, also known as ascites.3
Episodes of collapse or fainting
Episodes of collapse or fainting should always require veterinary attention. In dogs with heart disease, these episodes occur when the disease causes a lack of blood flow to the brain and the dog loses consciousness.3
Pulmonary edema in dogs
What causes heart murmurs in dogs?
A heart murmur can have various causes and is not always a sign of other illnesses. Further testing is usually required to look for an actual cause, especially for higher-level noises.
A heart murmur can occur in any dog, regardless of age, gender, size or breed. Structural abnormalities and extracardiac (outside the heart) disease are common causes. “Innocent” heart murmurs often occur that do not require treatment and can go away on their own. Large breed puppies are more susceptible to innocent heart murmurs, while small breeds are at higher risk for acquired heart murmurs.1
Abnormalities of the heart structure
Structural problems such as leaky valves or holes in the heart chamber can lead to improper blood flow. This creates turbulence, which can be heard as a heart murmur. Some structural abnormalities are present at birth, but others may develop later in life. The most common cardiac structure abnormalities include:
Mitral valve disease (also known as mitral regurgitation and more common in small breeds)1
Tricuspid valve disease
Subaortic or pulmonary stenosis (narrowing of the valves)
Patent ductus arteriosus (extra vessel present at birth)
Endocarditis (inflammation of the heart; sometimes caused by an infection)
Ventral septal defect (an opening in the wall between the lower chambers of the heart)
Atrial septal defect (an opening in the wall between the upper chambers of the heart)
Extracardiac diseases
Certain problems in the body can affect blood flow through the heart, even if the heart itself is functioning normally.
anemia
Heartworm disease
Infections in the body
Hyperthyroidism (this is rare in dogs)
Hypoproteinemia (low protein levels in the blood)
Innocent heart murmur
“Innocent” or physiological heart murmurs are benign, meaning they are not caused by a disease process. These murmurs are generally mild to moderate (Grade I-II). Puppies may have innocent heart murmurs that disappear with age.4
If your veterinarian detects a mild to moderate heart murmur in the absence of other signs, he or she may re-examine your puppy periodically to monitor the heart murmur rather than immediately recommending further diagnosis.4
How do veterinarians diagnose heart murmurs in dogs?
Heart murmurs are detected when your veterinarian hears an unusual noise while listening to your dog’s heart through a stethoscope. Mild or moderate noises may occur during routine veterinary visits in the absence of other symptoms, while severe noises may be accompanied by signs of more serious illnesses. Dogs with murmurs related to problems such as extracardiac disease or structural heart problems typically exhibit other symptoms that can help your veterinarian diagnose the cause.1
After taking a detailed medical history of your dog, your veterinarian will perform a thorough physical examination. When a heart murmur is heard, it is assigned a location (right or left) and an intensity level (from I to VI).
Your vet will then determine whether another illness is present. Several diagnostic tests are required to assess heart function and overall body health.
Chest x-rays to examine heart size and detaills of the heart and lungs.
Blood tests, a complete blood count, and a urinalysis are also often performed to assess organ health and cell count.2
Next, special cardiac tests may be needed to examine the heart more closely. Your pet doctor may refer you to a veterinary cardiologist for this exam. An electrocardiogram (EKG or EKG) measures electrical activity in the heart by displaying waveforms that can be analyzed to look for abnormalities. An echocardiogram is an ultrasound scan of the heart that shows the heartbeat and blood flow through the heart. The sonographer can measure the chambers and valves of the heart and look for abnormal blood flow patterns.2
How to Treat Heart Murmurs in Dogs
Because a heart murmur itself is not a disease but a sign of a possible disease, treatment depends on the underlying cause of the heart murmur (if any). An asymptomatic dog with a mild heart murmur may not require treatment. However, a moderate to severe murmur may require further action, especially if clinical signs are noted.
Once a diagnosis has been made, treatment recommendations can be discussed. Heart disease is usually treated with medication and supportive measures such as dietary restrictions or supplements. Some heart abnormalities require surgery to repair.1 Dogs with heart disease need routine follow-up visits with their veterinarian and/or cardiologist to monitor response to treatment and assess disease progression.
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Prognosis for dogs with heart murmurs
Some heart murmurs may disappear over time. Many innocent sounds in puppies disappear on their own as the dog grows. However, some serious conditions such as dilated cardiomyopathy can be serious or even fatal.
Congenital heart diseases can have significantly different prognosis – some can be corrected with surgery, others may require long-term treatment or be more serious.1 Your dog’s specific prognosis will depend on the cause of his heart murmur, which your veterinarian can diagnose to determine the correct treatment plan.
How to prevent heart murmurs
Most heart murmurs cannot be prevented, but early detection can allow your veterinarian to treat an underlying condition before it becomes serious. Because heart murmurs can go undetected without regular visits to the vet, dog owners should schedule checkups for their dogs at least once a year.
Always be sure to follow your veterinarian’s recommendations for treatment and aftercare. Speak to your veterinarian if you have difficulty adhering to recommendations, as consistent treatment may be critical to your dog’s survival.
While harmless heart murmurs and those caused by structural problems may not be preventable, the following tips can prevent some heart murmurs caused by extracardiac disease:
Regular teeth cleanings
Maintaining your dog’s dental health can be an important step in preventing heart disease such as endocarditis.1 Stick to regular professional dental cleanings at your veterinarian’s office and important home care by brushing your dog’s teeth regularly. Dental chews can also be helpful, but treats should be monitored to help your dog maintain a healthy weight.
Diet and nutrition
Gaining too much weight increases your dog’s risk of heart disease and other serious health problems. Since this is the most common preventable dog disease, it is also a way for owners to help prevent heart problems in their dogs.5 Feed your dog high-quality dog food and consult your veterinarian to determine the correct portion size based on your dog’s diet determine special needs.
Exercise
Exercising your dog regularly throughout his life is a helpful way to support heart health. Dogs with underlying medical conditions should have their exercise program monitored by a veterinarian to ensure their heart and lungs are able to support their activity levels.6