Heart Murmurs in Dogs

A routine check-up with the veterinarian will involve listening to the dog’s heart with a stethoscope. During this test, the veterinarian will make sure that the normal sounds of the heart are present as expected and any abnormal sounds are not. A heart murmur is an abnormal sound indicating turbulence in the flow of blood. While not a disease or condition itself, a heart murmur can be a sign of heart trouble, such as endocarditis, valve abnormalities, or stenosis (narrowing of the arteries).

A heart murmur can present as a number of different sounds, frequently as a “rumble” or burble, and are differentiated according to which stroke of the heart they are associated with (e.g. systole (filling stroke) and diastole (ejection stroke), or whether they are continuous. They are also ranked on intensity, or how loud they appear to be through the stethoscope, the quality (single frequency versus multiple), and whether they increase in intensity or decrease from the start of the murmur.

• Abnormality of the heart
• Swelling/inflammation of the heart
• Incomplete closing of a valve
• Narrowing of the arteries

A heart murmur is diagnosed by listening to the heart with a stethoscope, and using veterinary knowledge to properly categorize and describe the sound such that it can be compared with heart conditions matching the same sound. Many heart conditions are identifiable with a proper comparison of the murmur with additional symptoms. Murmurs are graded from I (very quiet, only audible with a stethoscope in a quiet room) to VI (very loud and accompanied by a vibration the veterinarian can feel on the chest).

Grading Scale

• Grade I—barely audible
• Grade II—soft, but able to be heard with a stethoscope
• Grade III—intermediate loudness; most murmurs which are related to the mechanics of blood circulation are at least grade III
• Grade IV—loud murmur that radiates widely - including opposite sites of the animals chest wall
• Grade V—very loud, audible with stethoscope barely touching the chest wall; commonly the vibration is strong enough to be felt through the chest wall
• Grade VI—very loud, audible with stethoscope barely touching the chest. The vibration is absolutely strong enough to be felt through the animal's chest wall

Medical imaging, such as MRI, X-ray, or ultrasound may be employed to image and diagnose a specific condition. Ultrasound in particular is a common, low-cost and non-invasive way to inspect a pet’s heart, also referred to as a cardiac echo. Conductive gel is applied to the pet’s skin, and an imaging wand is moved around the area, instantly showing a picture of the heart and surrounding tissue. This can be done in even a small veterinarian’s office.

A number of conditions can present with heart murmurs, such as a valve abnormality, swelling or inflammation of the heart. These can be detected with medical imaging such as ultrasound. Narrowing of the arteries and tumors on the heart tissue may be seen using ultrasound, but are better examined with an MRI or CT scan. These machines are larger and require your pet to physically enter the machine.

Young dogs occasionally have a faint Grade I heart murmur, which does not signify any illness and is a result of a growing cardiovascular system.

A heart murmur is an indicator of the condition of the heart and surrounding arteries. Treatment will vary, but usually is concerned with correcting the cause of the murmur. This may involve surgery in the case of a valve defect, or diet modification in the case of atherosclerosis (constricted arteries). Tumors of the heart may require chemotherapy in addition to surgical removal. Sometimes, small heart or valve defects can cause a quiet murmur, but if medical imaging reveals no serious defect, the condition need not be treated for a normal lifespan.

As mentioned previously, the murmur itself is not a condition and outlooks will vary based on the treatment. In general, checkups will be require to monitor the response to treatment and ensure the murmur has not changed or intensified.