What Are the Types of Heart Murmurs in Dogs?

Heart murmurs are generally classified by timing: systolic, diastolic, and continuous. 

Systolic Murmurs

This type of heart murmur in dogs happens when the heart is contracting and pumping blood out. They are the most common type, often detected during wellness checks. Systolic murmurs are often associated with mitral valve disease. 

Diastolic Murmurs

Diastolic murmurs happen when the heart is relaxing and filling with blood. They are much less common but are more serious. Diastolic murmurs often indicate abnormal blood flow into the heart, requiring further diagnostic testing.

Continuous Murmurs

These heart murmurs are heard throughout the entire heartbeat cycle, both during contraction and relaxation. They are generally linked to congenital heart defects, especially patent ductus arteriosus. Continuous murmurs are generally chronic and require medical treatment. 

What Are the Grades of Canine Heart Murmurs?

Our veterinarians grade them based on how loud they sound and how severe they are. 

What Are the Symptoms of Heart Murmurs in Dogs?

Some dogs may show no symptoms, especially in the earlier stages. However, certain signs may start to appear as the condition progresses. 

• Persistent Coughing. Chronic coughing may be possible, as it’s one of the most common signs of heart murmurs in dogs. It may worsen at night or after exercise. 

• Breathing Difficulties. You may notice rapid, labored, or shallow breathing, even if your dog is resting and not even exercising. 

• Exercise Intolerance. Dogs with heart problems often can’t keep up with their usual activity levels. They may get tired easily or become reluctant to exercise. 

• Weakness and Fainting. In severe cases, a dog with heart murmurs may experience weakness and even faint. This happens when the brain doesn’t get enough oxygen due to poor circulation. 

• Swollen Abdomen. A significant sign of advanced heart disease is a swollen abdomen due to fluid buildup. 

• Behavioral Changes. Some dogs may lose their appetite and appear lethargic.

What Causes Heart Murmurs in Dogs? 

Heart murmurs can be caused by turbulent blood flow within or near the dog’s heart. This results in faulty valves, structural defects, or even diseases that weaken the heart muscle. Here are the common conditions that may lead to heart murmurs. 

Mitral Valve Disease

MVD is a condition in which the valve thickens and becomes inefficient, causing the backward leakage of blood from the left ventricle into the left atrium during contraction. This causes the characteristic sound of a heart murmur in dogs. 

This is common in breeds such as Cavalier King Charles Spaniels, Dachshunds, Yorkshire Terriers, and other small dog breeds. 

Dilated Cardiomyopathy

DCM weakens the heart muscle, resulting in the enlargement of the heart chambers. This stretching prevents the mitral valves from closing properly, allowing blood to leak backward and causing the murmur. 

Dilated cardiomyopathy generally affects large dogs, including Doberman Pinschers, Boxers, Great Danes, and Saint Bernards. 

Congenital Defects

Congenital defects consist of structural abnormalities, such as narrowed valves, malformed chambers, or abnormal connections. These defects affect blood flow through the heart in a turbulent way, creating the murmur’s sound. 

Endocarditis

A bacterial infection that causes inflammation, structural damage, and improper valve closure. This results in the backward flow of blood, producing the sound. 

Heartworm Disease

Heartworm disease in dogs causes heart murmurs by creating physical obstructions and damaging the tricuspid valve. The large number of heartworms can physically restrict blood flow and inflame the heart’s structures. 

Anemia

Anemia can also cause heart murmurs in dogs by making the blood thinner and less viscous, resulting in turbulent blood flow through the heart chambers.