A heart murmur can occur in any dog regardless of its age, sex, size, or breed. While heart murmurs are not always an issue, they can be a sign of other serious problems in the body and may indicate that heart disease is present. Heart murmurs are detected by veterinarians as abnormal sounds during examinations. There are several reasons that may contribute to your vet noticing this sound while listening to your dog's heart through a stethoscope. Structural abnormalities and extracardiac conditions are common causes, and often, "innocent" heart murmurs occur that do not require treatment and can disappear on their own. Large-breed puppies are more prone to innocent heart murmurs, while small breeds are at higher risk for acquired heart murmurs.
Heart disease can lead to serious health problems when left untreated, so heart murmurs require veterinary attention to determine whether other diseases are present. Your vet may find an incidental murmur in your dog's heart during a routine wellness examination even if no symptoms are present. Since heart murmurs can go undetected without regular visits to the vet, it's important for dog owners to schedule check-ups for their dogs at least annually.
What Is a Heart Murmur?
A heart murmur is an abnormal heart sound that occurs when there is turbulent blood flow in the heart, which resembles a whooshing noise when listening with a stethoscope. While it's not a disease in itself, a heart murmur may indicate heart disease or another problem in the body.
Any disruption to the natural blood flow in the heart can cause turbulence that can be heard with a stethoscope. The heart has four chambers: the right atrium, the right ventricle, the left atrium, and the left ventricle. In a normally functioning heart, oxygen-depleted blood from the veins enters the right atrium and is pumped into the right ventricle. The blood flows through the artery of the lungs, becomes oxygen-saturated, and enters the left ventricle. This oxygenated blood is pumped through the left atrium, then goes out to the body through the arteries. Valves between each chamber and the blood vessels keep blood moving in the proper direction.
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 murmurs are quiet and may occur intermittently. Grade VI murmurs are the most severe. These are very loud when listening with a stethoscope and can usually be felt by placing the hands on the dog's chest. The higher the grade of a heart murmur, the greater the blood flow turbulence in the heart.
Symptoms of Heart Murmurs in Dogs
Dogs with heart murmurs may or may not exhibit any clinical signs of illness. Because a heart murmur is a sign of a possible heart problem but not an actual disease, the presence of other symptoms depends on the degree of underlying disease, if any. If your dog has a history of a heart murmur, keep an eye out for signs of severe problems like heart failure or moderate symptoms indicating that other diseases require further testing. The following symptoms are commonly seen in dogs with heart disease that can be indicated by a heart murmur:
Swelling of the heart can put pressure on the lungs and cause dogs with heart disease to cough. Coughing is a sign of many different types of heart disease, as various cardiovascular diseases can all lead to your dog's heart becoming enlarged.
Lethargy, Exercise Intolerance, or Weakness
Exercise intolerance is another common sign of cardiovascular disease in dogs. Your dog may become tired quickly after being active, appear weak, or act lethargic at home due to insufficient functioning of the heart.
Panting or Abnormal Breathing
Your dog may pant consistently or experience abnormal breathing. Breathing issues may affect dogs with heart disease more during the night while sleeping or when they stand up from laying down.
Pale gums are associated with more serious stages of heart disease in dogs. While this is also a sign of dental disease, if you notice that your dog's gums are any color other than pink, schedule an appointment with your veterinarian to determine the cause.
Dogs with heart disease may appear bloated in their bellies. This is caused by fluids pooling in the abdomen and may also be referred to as ascites.
Episodes of Collapse
Your dog collapsing should always warrant veterinary attention. In dogs with heart disease, these episodes happen when the illness causes a lack of blood flow to the brain (and ultimately, makes the dog lose consciousness).
Causes of Heart Murmurs
A heart murmur may occur for several reasons, and it is not always a sign of other diseases. Further diagnostics are typically needed in order to look for an actual cause, especially with higher-grade murmurs.
Heart Structure Abnormalities
Structural problems like leaky valves or holes in the chamber of the heart can cause improper blood flow. This creates turbulence which can be heard as a heart murmur. Some structural abnormalities are present at birth while others can develop later in life. Common heart structure abnormalities include:
- Mitral valve disease (also known as mitral insufficiency, and more common in small breeds)
- Tricuspid valve disease
- Subaortic or pulmonic stenosis (narrowing of valves)
- Patent ductus arteriosus (extra vessel present at birth)
- Endocarditis (inflammation in the heart; sometimes caused by an infection)
Certain problems in the body can affect the flow of blood through the heart, even if the heart itself is functioning normally.
- Heartworm disease
Innocent Heart Murmurs
"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 go away as they grow.
If your vet detects a mild to moderate heart murmur when no other signs are present, your vet may want to simply recheck your dog periodically to monitor the murmur rather than recommending further diagnostics right away.
Diagnosing Heart Murmurs in Dogs
Heart murmurs are detected when your veterinarian hears an abnormal whooshing sound while listening to your dog's heart through a stethoscope. Mild or moderate murmurs are typically found during routine veterinary appointments if no other symptoms are present, but severe murmurs are usually accompanied by signs of more serious diseases. Dogs with murmurs that are related to issues like extracardiac disease or structural heart problems typically show other symptoms that can help your veterinarian diagnose the cause.
After obtaining a detailed medical history from you regarding your dog, your veterinarian will perform a thorough physical examination. If a heart murmur is heard, it will be given a grade of intensity (from I to VI).
Your veterinarian will then determine if another disease is present. Several diagnostic tests are needed to assess heart function and overall body health. Blood chemistry, a complete blood count, and a urinalysis to assess organ health and cell counts will be performed. Radiographs (X-rays) of the chest will be needed to look at heart size and details of the heart and lungs.
Specialized heart tests may be needed next to get a closer look at the heart. Your primary veterinarian may refer you to a veterinary cardiologist for this testing. An electrocardiogram (ECG or EKG) measures electrical activity in the heart by displaying waveforms that can be analyzed to look for abnormalities. An echocardiogram is an ultrasound of the heart that shows the heart beating as well as the blood flow through the heart. The sonographer can measure the chambers and valves of the heart as well as look for abnormal blood flow patterns.
Treatment & Prevention
Because a heart murmur is not a disease itself, but a sign of potential disease, the treatment will depend on the underlying cause of the heart murmur, if any. An asymptomatic dog with a mild heart murmur may not need any treatment. However, a moderate to severe murmur warrants further action, especially if clinical signs are noted.
Once a diagnosis has been made, treatment recommendations can be discussed. Some heart abnormalities will require surgery to repair. Other conditions may be treated with specialized diets or medications in addition to supportive care by the owner. Dogs with heart disease will need routine follow-up visits to their primary vet and/or cardiologist to monitor the response to treatment and evaluate the progression of the disease.
Prognosis for Dogs With Heart Murmurs
Some heart murmurs can resolve over time. Many innocent murmurs in puppies will disappear on their own as the dog grows, but some serious conditions like dilated cardiomyopathy can be serious or even fatal. Congenital heart diseases can have significantly different prognoses—some may be corrected through surgery, but others may require long-term treatment or be more severe. Your dog's specific prognosis will depend on the cause of its heart murmur, which your veterinarian can diagnose to determine the proper treatment plan.
How to Prevent Heart Murmurs
Not all heart murmurs cannot be prevented, but early detection can enable your veterinarian to treat an underlying disease before it becomes serious. Always be sure to follow your vet's recommendations for treatment and follow-up. Talk to your vet if you are having trouble complying with recommendations, as consistency in treatment can be essential to your dog's survival. While innocent murmurs and those caused by structural problems may not be prevented, the following methods can prevent some heart murmurs caused by extracardiac disease:
Regular Dental Cleanings
Maintaining your dog's dental health can be an essential way to prevent heart diseases like endocarditis. Keep up with consistent dental cleanings at your veterinarian's office along with important at-home care by brushing your dog's teeth regularly. Dental chews can also be beneficial, but treats should be monitored to help your dog maintain a healthy weight.
Diet and Nutrition
Gaining too much weight puts your dog at higher risk for heart disease along with other serious health conditions. Since this is the most common preventable canine disease, it's also one way that owners can help prevent heart problems in their dogs. Feed your dog a diet of high-quality dog food and consult your veterinarian to determine proper portion sizes based on your dog's specific needs.
Exercising with your dog regularly throughout its life is a helpful way to support heart health. Dogs with underlying conditions should have their exercise routine overseen by a veterinarian to ensure their hearts and lungs are able to support their activity level.
Heart Murmurs in Dogs. VCA Animal Hospitals.
- Côté, Etienne, et al. Management of Incidentally Detected Heart Murmurs in Dogs and Cats. Journal of Veterinary Cardiology: The Official Journal of the European Society of Veterinary Cardiology, vol. 17, no. 4, 2015, pp. 245–261, doi: 10.2460/javma.246.10.1076
Diagnosis of Cardiovascular Disease in Dogs. Merck Veterinary Manual.
Szatmári, V., et al. Innocent Cardiac Murmur in Puppies: Prevalence, Correlation with Hematocrit, and Auscultation Characteristics. Journal of Veterinary Internal Medicine, vol. 29, no. 6, 2015, pp. 1524–1528, doi: 10.1111/jvim.13632
Obesity in Dogs. VCA Animal Hospitals.
Healthy Exercise for Dogs. VCA Animal Hospitals.