Heart murmurs in dogs are abnormal sounds caused by turbulent blood flow through the heart. They are typically heard through a stethoscope during veterinary examinations. While a heart murmur is not always a concern, it can indicate other serious problems in the body, particularly heart disease. Because heart disease can lead to serious health problems when left untreated, heart murmurs require veterinary attention to determine whether other diseases are present. Here's what you need to know if your veterinarian has detected a heart murmur in your dog.

 

What Is a Heart Murmur?

A heart murmur is an abnormal heart sound that resembles a whooshing noise when listening with a stethoscope. It occurs when there is turbulent blood flow in the heart. A heart murmur is not a disease in itself, but it may signify heart disease or another problem in the body.

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 atrium. This oxygenated blood is pumped through the left ventricle and goes out to the body through the arteries. Valves between each chamber and the blood vessels keep blood moving in the proper direction. Any disruption to the natural blood flow in the heart can cause turbulence that can be heard with a stethoscope.

Heart Murmur Grades 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 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. Your vet may find an incidental murmur while listening to your dog's heart during a routine wellness examination even if no symptoms are present. 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 testing should be performed. The following symptoms may be seen in dogs with heart disease that can be indicated by a heart murmur:

  • Coughing: Swelling of the heart can lead to pressure on the airway and turbulent blood flow can also lead to fluid backing up into the lungs. Both are common causes for coughing in dogs with heart disease.
  • Lethargy, Exercise Intolerance, or Weakness: Your dog may become tired easily during exercise or activities. They may also appear weak or lethargic at home due to insufficient functioning of the heart.
  • Abnormal Breathing or Panting: Dogs with heart problems may breathe rapidly, experience labored breathing, or pant more than usual. Breathing issues may affect dogs with heart disease more noticeably during the night while sleeping or when they stand up from lying down.
  • Pale Gums: Pale gums are associated with more serious stages of heart disease in dogs, but it can also be a sign of many other diseases. If you notice that your dog's gums are any color other than pink, schedule an appointment with your veterinarian to determine the cause.
  • Distended Abdomen: Dogs with right-sided heart disease may have abdominal distention that makes them appear bloated in their bellies. This is caused by fluids pooling in the abdomen, which is also referred to as ascites.
  • Episodes of Collapse or Fainting: Episodes of collapse or fainting 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, making the dog lose consciousness.

What Causes Heart Murmurs in Dogs?

A heart murmur may occur for several reasons, and it is not always a sign of other diseases. Further testing is typically needed to look for an actual cause, especially with higher-grade murmurs.

A heart murmur can occur in any dog regardless of age, sex, size, or breed. Structural abnormalities and extracardiac (outside the heart) conditions are common causes. 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 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)
  • Ventral septal defect (an opening in the wall between the heart's lower chambers)
  • Atrial septal defect (an opening in the wall between the heart's upper chambers)
Extracardiac Conditions

Certain problems in the body can affect the flow of blood 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 blood protein levels)
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 veterinarian detects a mild to moderate heart murmur when no other signs are present, they may recheck your puppy periodically to monitor the murmur rather than recommending further diagnostics right away.

How Do Vets Diagnose 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 can be found during routine veterinary appointments if no other symptoms are present, while severe murmurs may be 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 location (right or left-sided) and 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:

  • X-rays of the chest to look at heart size and details of the heart and lungs.
  • Blood chemistry, a complete blood count, and a urinalysis to assess organ health and cell counts are also commonly performed.
  • 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.

How to Treat Heart Murmurs in Dogs

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 may warrant further action, especially if clinical signs are noted.

Once a diagnosis has been made, treatment recommendations can be discussed. Heart disease is commonly treated with medications and supportive care like dietary restrictions or supplements. Some heart abnormalities require surgery to repair. Dogs with heart disease will need routine follow-up visits with 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. However, some serious conditions, such as 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

Most heart murmurs cannot be prevented, but early detection can enable your veterinarian to treat an underlying disease before it becomes serious. Since heart murmurs can go undetected without regular visits to the vet, dog owners should schedule check-ups for their dogs at least annually.

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 tips 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 professional 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.
  • Exercise: 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.