Heart Murmurs in Dogs

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Understanding Canine Heart Murmurs 

Heart murmurs are auscultatory sounds created by turbulent or disturbed blood flow through the heart or vasculature. They can be heard over any region of the heart and can be associated with a variety of causes. Murmurs can be caused by congenital malformations of the heart, acquired heart disease, or by other diseases that can affect the heart but are not caused by an underlying heart disease.

Murmurs can indicate abnormal heart valve, heart muscle disease, a congenital patency (an abnormal opening) between sides of the heart, anemia, heartworm disease, abnormal thyroid function, or be “functional” which does not indicate heart disease. Some murmurs heard in puppies and kittens will disappear as the pet ages (usually < 4 months).

Murmurs are often classified based by their location, timing, duration, character and grade. For example:

  • Location refers to the area of the heart in which the sound appears to originate. It is usually described by the sounds proximity to a valve area such as the aortic, mitral, tricuspid or pulmonic or relative to body structures such as left apex or sternal border.
  • Timing refers to when the murmur occurs during the heart beat cycle. It is most often described as systolic, diastolic or continuous.
  • Duration refers to how long the sound lasts within the timing phase.
  • Character of the murmur refers to the quality of the sound such as if the murmur gets louder than softer during the heart’s cycle. Words often used to describe the murmurs “character” includes plateau, regurgitant type, crescendo, decrescendo, crescendo-decrescendo, ejection, or machinery.
  • Grade refers to the intensity of the sound. The scale is generally from 1 to 6 with 1 being the softest and 6 being the loudest. Some murmurs are accompanied by a “thrill” which indicates that the murmur is so loud it causes a palpable vibration that can be felt over the chest wall.

    The classification of the murmur is used to help determine possible causes for the murmur, however, this can be difficult. Additional tests may be required such as an echocardiogram.

  • How are Murmurs Created?

    Each heartbeat originates as an electrical impulse and eventually generates a muscular movement. The heart is a muscle that’s “job” is to pump blood. Blood is pumped from the body to the heart, processed through the lungs, returned back to the heart and pumped out to the body. As the blood is pumped, it goes through four different parts of the heart or heart chambers. Between these chambers are “valves”. A valve is a membrane that opens and closes to prevent backward flow of blood.

    Heart murmurs can be caused from either heart muscle or valve abnormalities. If either of these structures do not function properly, the flow of blood is disturbed. This disturbance can cause “turbulence” in the blood flow that creates an abnormal sound that we refer to as a “murmur”.

    Heart murmurs may affect dogs of any age or sex. They may also affect any breed, however some breeds are more prone to heart disease.

    The prognosis (outlook) for animals with heart murmurs depends on the underlying cause of the murmur such as the type and extent of any existing heart disease.

    What to Watch For

    A murmur is an abnormal heart sound and is found only by listening to the heart. Occasionally a vibration or “thrill” can be felt over the heart. Signs of heart disease or secondary problems in dogs that may be associated with the mumur may include:

  • Some pets have no symptoms
  • Weakness
  • Collapse
  • Slow heart rate
  • Fast heart rate
  • Erratic heart rate
  • Difficulty breathing
  • Lack of appetite
  • Coughing
  • Diagnosis of a Heart Murmur in Dogs

    When a murmur is present, the goal is to determine the underlying cause for the murmur. Tests may include blood work, urinalysis, chest radiographs and an echocardiogram.

  • The “gold standard” for diagnosing the underlying cause of a heart murmur is a cardiac ultrasound (echocardiogram). It is performed to evaluate cardiac and valve function and identify underlying heart disease. Murmurs that occur in puppies and kittens can be very difficult to diagnose even for the most experienced veterinarians. Many pets may be referred to a board certified veterinary cardiologist for evaluation.
  • Thoracic (chest) radiographs (X-rays) may help determine if heart disease or heart failure is present.
  • Blood work, including a complete blood count and biochemical profile, may be performed to look for any underlying abnormalities. Some dogs may be anemic, have an elevated white blood cell count, or have other organ dysfunction.

    How aggressively one pursues the underlying cause of the murmur depends upon the likelihood of a serious underlying problem and if there are any other associated symptoms indicating the probability of heart disease.

    Possible Causes of Murmurs

    Murmurs can be caused by a variety of cardiac and noncardiac diseases. Some diseases that can affect the heart but are not caused by an underlying heart disease.

    Cardiac Causes of a Murmur

  • Subaortic stenosis
  • Pulmonary stenosis
  • Septal defects
  • Atrioventricular dysplasia
  • Tetralogy of Fallot
  • Mitral Stenosis
  • Aortic Valvular Insufficiency
  • Pulmonic Valvular insufficiency
  • Patent Ductus Arteriosus
  • Arteriovenous fistula
  • Cardiomyopathy
  • Endocardiosis or Chronic Valvular Heart Disease

    Noncardiac Causes of a Murmur

  • Fever
  • Anemia
  • Infection causing endocarditis
  • Thyroid disease
  • Heartworm disease
  • Pericardial disease
  • Tumors
  • Obesity
  • Cachexia
  • Pregnancy
  • Treatment of Heart Murmurs in Dogs

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