• A heart murmur is an abnormal sound that a veterinarian hears when listening to the heart through a stethoscope.
  • A murmur is not always a cause for concern, but it can be an indication of heart disease, so other diagnostic tests may be warranted.
  • Found in young puppies, innocent murmurs are essentially harmless and usually disappear by 4 months of age.
  • Signs of heart disease in dogs include coughing, difficulty breathing, exercise intolerance, collapse, and abdominal distention.
  • To diagnose the cause of a murmur, your veterinarian may recommend tests such as blood tests, chest radiographs (x-rays), and echocardiograms.

What Is a Heart Murmur?

A heart murmur is an abnormal sound that a veterinarian hears when listening to a dog’s heart through a stethoscope. Normally, a veterinarian hears two sounds, a “lub” and a “dub,” which are the sounds of the heart valves closing as blood circulates through the heart. An additional “whooshing” sound, known as a heart murmur, is usually associated with a disturbance of the smooth blood flow through the heart.

Veterinarians rank the intensity or loudness of a heart murmur in grades from one to six, with one being barely audible and six being the loudest. There is also a one-to-five ranking system that works the same way. These grades do not necessarily correlate with the severity of the heart condition; they are merely one of several ways that veterinarians attempt to characterize the murmur.

A heart murmur is not always a cause for concern, but it may be an indication of a heart problem. Depending on the dog’s condition, your veterinarian may want to perform additional diagnostic tests to determine the cause of the murmur.

What Causes a Heart Murmur?

Heart murmurs are caused by any number of conditions that can create turbulence in the flow of blood through the heart. In dogs, common causes for heart murmurs include:

  • Heart valve deficiencies or blockages
  • Defects in the heart walls
  • Dilated cardiomyopathy (weakening of the heart muscle walls)
  • Heartworm disease
  • Endocarditis (an infection of the heart valves)
  • Tumors

What Is an Innocent Murmur?

Occasionally, veterinarians may detect a heart murmur in a young puppy. While this may indicate the presence of a congenital heart condition (a defect that the puppy was born with), in many cases it is an innocent murmur, meaning that it is not related to a heart problem. These murmurs usually disappear by the time the animal is about 4 months of age. If a murmur does not resolve, your veterinarian may recommend diagnostic testing to investigate it further.

What Are Other Signs of a Heart Condition?

Not all dogs with a heart condition show outward signs. However, if you have been told that your dog has a heart murmur, you should watch for signs such as:

  • Coughing
  • Difficult or rapid breathing
  • Congestion or “noisy” breathing
  • Exercise intolerance (reluctance to exercise)
  • Weakness or lethargy (tiredness)
  • Fainting episodes
  • Gray or blue gums
  • Abdominal distention (a “pot-bellied” appearance)
  • Collapse

If your dog displays any of these signs, call your veterinarian for advice, or schedule a veterinary exam.

What Diagnostic Tests May Be Necessary?

To determine the cause of a heart murmur, your veterinarian may recommend a number of tests, such as:

  • Blood tests, including heartworm tests
  • Chest radiographs (x-rays) to assess the heart, blood vessels, and lungs
  • An electrocardiogram (ECG)
  • An echocardiogram (an ultrasound exam to evaluate heart structure and function)
  • Blood pressure tests

How Are Heart Murmurs Treated?

Treatment depends on the cause of the heart murmur and your dog’s condition. If your dog is not showing any signs of heart disease other than the murmur, your veterinarian may prefer to monitor your dog and provide treatment only if signs occur.

In some cases, such as when heart murmurs are caused by heartworm disease, treatment may resolve the heart murmur completely. If the murmur is caused by a congenital condition, surgery may be recommended. In other cases, the heart murmur may remain, but medications can help make your dog more comfortable and improve your pet’s longevity.