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:
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:
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.
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
Noncardiac Causes of a Murmur