Heart Murmurs in Dogs

Although dogs and humans differ in many respects, they also have a lot in common physiologically. A case in point is the heart. For both species, this vital muscle is what ensures that blood can flow throughout the body. Both people and canines can experience heart-related conditions that can sometimes be serious. One of these is a heart murmur. Should your vet discover that your furry friend has one of these, you of course want to gain all the knowledge you can about this physical condition.

What is a Heart Murmur?

Like humans, dogs’ hearts have four chambers – two ventricles and two atria. A one-way valve between each of these chambers opens and closes as the blood flows, ensuring that the blood only goes in the right direction. The lub-dub sound we associate with the canine or human heartbeat results from the maneuverings of these valves. If, however, the heartbeat does not sound normal and contains an additional whooshing noise stemming from turbulence in the blood flow, your dog will be diagnosed with a heart murmur.

Characteristics of Heart Murmurs in Dogs

According to Dr. Claire Wiley, VMD, DACVIM, and Executive Director of the AKC DNA Program, there are three aspects that characterize heart murmurs in dogs:

• Intensity. This is measured via a system that ranges from Grade I (the mildest) to grade V (the most severe). A grade I murmur is barely audible, often only perceivable in a quiet room. On the other hand, a grade V murmur is so loud that it can be heard with a stethoscope placed several inches away from the dog’s chest.
• Timing. A systolic murmur occurs when the heart is contracting, while a diastolic one happens as the heart relaxes.
• The side of the chest where the murmur is heard.

Although some canine heart murmurs can be serious, a good number of them are what is known as innocent or benign. These so-called physiologic murmurs do not require treatment. In all cases, however, it is important that your dog’s heart murmur be thoroughly evaluated by a veterinarian to identify the cause and to determine if it requires any sort of medical intervention.

Puppies and Heart Murmurs

An estimated 28 percent of puppies under six months of age have an “innocent” heart murmur. In athletic breeds such as Whippets, that number can rise to 58 percent. For many very young dogs, murmurs stem from increases in blood flow after exercise or excitement. For most puppies with innocent heart murmurs, the condition resolves itself as the dog matures, requiring no treatment whatsoever. Nevertheless, it is important to monitor your puppy to ensure that the murmur disappears as expected and is not accompanied by other symptoms that warrant attention.

What Causes Heart Murmurs in Dogs?

Those heart murmurs that are not benign may be caused by a number of factors. These include the following:

• Medical conditions such as anemia that affect the thickness of the blood.
• Medical conditions such as hyperthyroidism that increase cardiac output.
• Structural defects in the heart. These can include aortic stenosis, congenital heart defects, holes in the heart and hypertrophic cardiomyopathy that causes the heart muscle to become thickened or enlarged.
• Cardiac infections.
• Mitral valve disease. More common in older small-breed dogs, this is characterized by blood leaking back through the mitral valve (between the left ventricle and left atrium). Usually, a heart murmur is the first clinical sign of this disease, which can eventually advance to congestive heart failure and death.

How Does Your Veterinarian Diagnose a Heart Murmur in Your Dog?

Protecting your dog’s cardiac health is one of the primary reasons for receiving regular checkups from your veterinarian. Detecting a heart murmur as soon as possible, for example, can enable your vet to diagnose mitral valve disease in its early stages, allowing for medical intervention that can prolong your dog’s life.

The preliminary diagnosis of a heart murmur can take place right in the doctor’s office. Your vet will use a stethoscope on both sides of your dog’s chest to monitor the heartbeat. If a murmur is suspected, a board-certified veterinary cardiologist can confirm your doctor’s initial suspicion via an echocardiogram. This is an ultrasound that allows for full visualization of the entire heart, including the valves and chambers.

How is a Dogs Heart Murmur Treated?

As we stated above, innocent heart murmurs and many found in growing puppies need no ongoing medical intervention. However, other murmurs do require intervention and monitoring on a regular basis. Exactly what treatment your dog receives will depend on the underlying cause of the murmur. Options include regular cardiac monitoring, special diets, medications or surgery to repair your dog’s heart defect.

For some dogs, a heart murmur has little or no impact on their health. For others, this condition can have a dramatic effect on the quality or duration of their life. Just as is the case with humans, each dog is unique. That’s why it is so important to discuss your pup’s heart murmur and its treatment with your veterinarian. Once you begin this important conversation, you will have the opportunity to ask questions and to proceed with the customized care that is best for your canine companion.