Fri, 04/12/2024 - 11:42pm

Heart Murmurs

From grading to treatment, everything you need to know

My veterinarian says my dog has a heart murmur. What does that mean?


A heart murmur is an abnormal sound that can be heard with a stethoscope when listening to the heart. Like people, a dog’s heart should have two distinct heart sounds: lub-dub, lub-dub, lub-dub. When an additional “whooshing” sound is heard between the normal heart sounds, it is called a heart murmur.

The murmur will be heard when there is turbulent blood flow within the heart. Some murmurs, especially those found in young puppies, can be “innocent” or “physiologic,” and will not negatively affect the dog’s health. Young puppies with innocent murmurs usually outgrow them by about five months of age.

Murmurs that persist should be evaluated by a veterinarian. This may indicate the presence of a congenital heart defect or other heart disease.


What causes a heart murmur in dogs?


Anything that changes the blood flow through the heart, causing the blood to pass through at increased speed and pressure, can cause a murmur to be heard. The most common causes are leaks in the heart valves and defects in the heart muscle walls, such as a ventricular septal defect.

Other causes include infection of the heart valves (endocarditis), narrowing of the pulmonary valve (pulmonic stenosis), narrowing involving the aortic valve (aortic stenosis), or the presence of an extra vessel connecting the great arteries (patent ductus arteriosus). Thickening of the heart valves or weakening of the heart muscle, such as occurs with dilated cardiomyopathy, can also produce a heart murmur.


How does the loudness of the murmur correlate with the severity of the heart disease present?


Murmurs are graded on a scale that refers to their loudness. This scale is somewhat subjective, since every veterinarian hears things differently, but it is useful to describe murmurs and monitor them over time.

Quiet murmurs may still represent severe heart disease, while loud murmurs may not cause any symptoms. Further investigation into the cause of the murmur is useful to guide treatment recommendations and provide a prognosis for future health.

Grade 1: Barely audible – the least serious type of heart murmur

Grade 2: Soft murmur, but easily heard with a stethoscope

Grade 3: Intermediate loudness, same intensity as heart sounds

Grade 4: Loud murmur that can be heard on both sides of the chest

Grade 5: Loud murmur with a thrill (vibration) that can be felt with the hand against the chest

Grade 6: Very loud murmur with a thrill that can be heard without the stethoscope


What are the signs of heart murmurs in dogs?


The symptoms of a heart murmur largely depend on the underlying heart condition that is affecting the dog. Many dogs with heart murmurs have no symptoms, especially when the murmur is a Grade 1 to 3. Since many heart murmurs develop in older dogs, owners often think they are slowing down due to age, when heart disease is actually contributing to their change in energy.

Some common symptoms of heart disease include labored breathing, persistent hacking cough, irregular heartbeat, lack of energy or appetite, blue gums, and collapsing or fainting.


What diseases cause heart murmurs in dogs?


There is a wide range of diseases that can cause a heart murmur in dogs. Most commonly, heart murmurs in small dogs are caused by a leaky mitral valve, which is the heart valve between the left atrium and left ventricle. The mitral valve allows blood to flow from the left atrium to the left ventricle, but does not allow for blood to flow back into the left atrium. Sometimes as a dog ages, the valve deteriorates, which causes blood to leak backward. This condition is known as chronic valve disease, degenerative mitral valve disease or endocardiosis.

In large-breed dogs, heart murmurs are often caused by a disease called dilated cardiomyopathy with a subsequent leaky mitral valve. Dilated cardiomyopathy is a disease that causes the muscles in the pumping chamber of the heart to become weakened and decreases the contraction strength of the heart.

There is a range of issues that can cause a murmur. Your veterinarian will be able to run the proper diagnostic tests to assess your dog’s heart and determine the cause of the murmur. These tests would include radiographs of the chest and abdomen, an electrocardiogram (EKG) and an echocardiogram, which is an ultrasound examination of the heart.


Can my dog’s heart murmur cause a heart attack?


Signs of a heart attack in people include chest pain, shortness of breath and weakness. Most human heart attacks occur when an artery is blocked and the heart cannot continue to pump blood. Luckily, this same type of disease does not occur in dogs.

In some cases, dogs with heart disease will experience fainting, which is called syncope. These episodes can resemble a heart attack, but do not often cause permanent damage and dogs recover quickly.


What are the treatment options for dogs with heart murmurs?


Treatment is designed to relieve the issues associated with the heart disease related to the murmur. Some dogs with heart murmurs live normal lives and never require treatment. Others with more severe disease will benefit from treatment, which can range from lifelong oral medications to surgery.

Depending on the cause of the murmur, treatment may sometimes resolve the murmur. For example, if your dog’s heart murmur is diagnosed with a birth defect known as patent ductus arteriosus, surgery can correct this abnormality, eliminate the heart murmur and provide a normal life expectancy. Investigating the cause of a murmur with a veterinary cardiologist is important in order to determine the best course of action.


What is the prognosis for dogs with heart murmurs?


The prognosis largely depends on the underlying cause of the murmur. For innocent murmurs that don’t require treatment, the prognosis is generally excellent. Heart murmurs caused by a functional problem that can be treated may resolve over time.

For dogs that have a leaky mitral valve, long-term medication can help prolong their lives and improve their quality of life. The prognosis for a dog with dilated cardiomyopathy varies. If the dog is already showing signs of heart failure, unfortunately the prognosis is poor.

The prognosis for dogs born with congenital heart defects depends on whether the defect can be surgically corrected. If it can be, the prognosis is usually very good.

Will a healthy diet and exercise reduce my dog’s risk of developing heart disease when a murmur is present?

With the most common form of heart disease in humans, cholesterol or plaque accumulates, resulting in narrowing or blocking of the arteries in the heart. This can lead to heart attacks or strokes. In order to prevent high cholesterol, people are instructed to avoid fatty foods and exercise frequently.

Your dog’s heart disease is not caused by plaque in his arteries. Heart disease in dogs affects either the heart muscle or the heart valves. While a balanced diet that is not grain-free is necessary to your dog’s health, the standard human “heart-healthy” diet will not prevent your dog from developing heart disease.

Because heart disease in dogs is so different from that of humans, vigorous aerobic exercise such as running can actually put more strain on your dog’s heart. Based on diagnostic findings, your veterinary cardiologist may recommend reducing or limiting your dog’s activity to avoid overworking the heart.



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