Heart Murmurs in Cats

Heart Murmurs in Cats

By: Dr. Debra Primovic

Section: Overview

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 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 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.

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