A murmur is caused by turbulent or fast blood flow within the heart or associated vessels. Such turbulence causes a “whooshing” sound, or what is termed a “murmur.”
There are numerous situations that result in a murmur. Some murmurs are benign and are not associated with any structural heart disease. Other murmurs are caused by abnormal blood flow associated with a variety of cardiac diseases, including abnormal heart valves and different congenital defects.
Soft, “innocent” murmurs are commonly heard in young puppies and kittens. These murmurs are not associated with any cardiac disease and should disappear by approximately four months of age.
Adult animals may have similar murmurs caused by physiologic conditions such as stress or fever. Such functional murmurs are benign and do not require any specific cardiac treatment.
Congenital heart defects are commonly associated with loud murmurs in dogs and cats. A loud murmur in a kitten or puppy is never “innocent,” and a referral should be made to a Cardiologist for further evaluation.
Specialized diagnostics tests, such as an echocardiogram (ultrasound of the heart), are used to diagnose congenital defects and determine prognosis and possible treatments.
The treatment of congenital heart disease depends on the type of defect. Some defects are managed medically while others are amenable to surgical intervention.
One of the most common congenital defects found in dogs that results in a very loud murmur is a patent ductus arteriosus (PDA).
The ductus arteriosus is a blood vessel normally present in the fetus that should close following birth. When this vessel remains open after birth, it results in the shunting of a large amount of blood through the lungs, causing increased work for the heart. Without treatment, this defect can lead to congestive heart failure (fluid in the lungs).
This congenital defect can be treated with surgery in which the vessel is tied off or with interventional catheterization procedure, whereby the vessel is closed with an implantable device.
The most common cause of a murmur in older dogs is degenerative valve disease (endocardiosis).
This disease is caused by an age-related thickening of the valves on the right and left sides of the heart. As a result of this thickening, the valves cannot close properly and begin to leak.
This leakage of blood backward as the heart contracts causes an audible murmur. As the leakage worsens, the heart enlarges or dilates, eventually leading to congestive heart failure. Although there is no cure for this condition, it can also be managed for a period of time with various medications.
The most common cardiac disease associated with a murmur in adult cats is a primary disease of the cardiac muscle (hypertrophic cardiomyopathy).
This disease results in thickening of the heart muscle and abnormal function of the heart. Although many patients remain free of clinical signs for years, some cats develop signs related to congestive heart failure or paralysis of limbs from a clot event.
Diagnosis of this disease requires echocardiography. Since feline murmurs are also commonly caused by noncardiac diseases, including high blood pressure and thyroid disease, other testing may also be required.
Routine examination by your pet’s regular veterinarian is important for identification of cardiac murmurs. Once a heart murmur is heard in a pet, your veterinarian can explain the options for further testing. Such recommendations might include chest x-rays, an electrocardiogram (ECG), or a referral to a veterinary Cardiologist for more advanced imaging.
This column is provided by the faculty of the OSU Boren Veterinary Medical Teaching Hospital. The large volume of questions does not allow us to directly respond to specific email questions so please watch for your answer in the column. Email your questions for the column to
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