The term “heart murmur” describes any of several abnormal sounds heard by your veterinarian during your pet’s heartbeat cycle. Caused by turbulent blood flow in the heart, murmurs can be heard with a stethoscope, and are characterized as a “whooshing” or “swishing” heart sound.
A heart murmur is a sign of turbulent blood flow, not a diagnosis! Your veterinarian may recommend seeing a cardiologist to determine if your pet’s murmur is innocent, indicative of a congenital problem (something your pet has had since birth), or indicative of acquired heart disease.
Murmurs are often classified on a I-VI scale based on the loudness of the murmur. The loudness of a murmur reflects the amount of turbulence that is present in the heart.
Grade I — barely audible after careful listening.
Grade II — soft, but easily heard.
Grade III — intermediate loudness, well localized. Most significant murmurs are Grade III or louder.
Grade IV — loud murmur that radiates widely, often including opposite side of chest
Grade V — very loud, audible with stethoscope barely touching the chest; the vibration is also strong enough to be felt through your pet’s chest wall with the hand.
Grade VI — very loud, audible with stethoscope not touching the chest; the vibration is also strong enough to be felt through your pet’s chest wall with the hand.
The loudness of a heart murmur does not always correlate with the severity of your pet’s heart condition. An echocardiogram, or ultrasound of the heart, allows the cardiologist to determine where the heart murmur originates from, and identify the underlying cause of turbulent blood flow.