Heart Murmurs in Healthy Dogs

Physiological heart murmurs (PHM) are sounds produced by blood flow in the absence of structural heart and great vessel abnormalities. They may occur in young dogs less than 6 months of age (“innocent” murmurs), or as a result of anemia, fever, or systemic hypertension (“functional” murmurs). Adult PHMs are more common in some breeds (eg, boxers) and may be attributed to increased sympathetic tone (eg, secondary to anxiety). 

This prospective study sought to determine the prevalence of PHMs in healthy young adult dogs (1-5 years of age) of various breeds presented for vaccination. Of 109 client-owned dogs evaluated, 95 completed the study. Dogs underwent physical examination, urinalysis, CBC, and blood pressure measurement to confirm healthy status. Cardiac auscultations were performed by 3 independent examiners. Dogs with heart murmurs underwent echocardiographic examination to screen for structural cardiovascular abnormalities. 

Prevalence of PHMs varied from 6% to 12% depending on the echocardiographic criteria used to exclude heart and great vessel abnormalities. All PHMs were systolic and low-grade (I-III/VI). Epidemiological features of dogs with PHMs were not different from dogs without murmurs. The authors noted the biggest challenge was distinguishing between physiological and pathological murmurs because of varying echocardiographic criteria for normality. They concluded that PHMs are relatively common in healthy young adult dogs and may not be limited to specific breeds.

Commentary 

Primary care veterinarians often discover new murmurs on routine wellness examinations. When a murmur is noted in a young, healthy dog, recommending further advanced diagnostics may cause owner anxiety as well as additional expenses, including referral for echocardiography. This paper helped quantify the presence of physiologic or “innocent” murmurs vs those heard because of underlying disease in young, otherwise healthy dogs. The location and grade of these physiologic murmurs were consistently found to be systolic, low-grade, and louder over the left heart base. In this study, echocardiographic abnormalities were detected in half of dogs with heart murmurs. Even with echocardiography, it may be difficult to distinguish between physiologic and mild pathologic heart murmurs, including subaortic stenosis, systolic pulmonary hypertension, and mild mitral regurgitation. More information about the prevalence of innocent murmurs in this dog population will help guide the discussion of whether to recommend advanced diagnostics.—Elizabeth Alvarez, DVM, DABVP