Heart murmurs are detected when a veterinarian listens to a dog’s heart and hears a whooshing sound. It’s not always a reason for concern, but it can be. In dogs, common causes include heart valve problems, heart defects, tumours, heartworm disease, or weakening of the heart muscle. If your dog has difficulty breathing, sounds congested or coughs, has a pot belly, faints, or suddenly collapses, he could have a heart condition.


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 or other noise, known as a heart murmur, is usually associated with a disturbance of the normally smooth flow of blood through the heart. Though it’s not considered normal, a heart murmur is not always a cause for concern. It may, however, be an indication of a heart problem. Depending on your dog’s condition, the veterinarian may want to perform additional diagnostic tests to determine the cause of the murmur.

Symptoms and Identification

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 growths called endocardiosis

• Defects in the heart wall • Endocarditis (an infection of the heart valves)

• Tumours

• Caval syndrome as a serious consequence of heartworm disease

Occasionally, a veterinarian detects a heart murmur in a young puppy. Though this may indicate the presence of a congenital heart condition (a defect the puppy was born with), in many cases it is what is called 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.

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

• Grey or blue gums

• Abdominal distention (a pot-bellied appearance)

• Collapse

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

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

• 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


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. 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.

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