The First Time You Detect a Grade II Heart Murmur in an Asymptomatic Dog
As veterinarians, heart murmurs are among the most common—and nuanced—findings we encounter on physical examination. A grade II/VI systolic murmur in an otherwise normal, asymptomatic dog presents a familiar clinical crossroads: the patient appears well, yet the auscultatory finding raises legitimate questions about underlying cardiac disease, future risk, and the appropriate next step.
From a cardiology-informed perspective, the goal at this moment is not immediate intervention, but accurate risk stratification, thoughtful documentation, and timely diagnostic decision-making. The approach should balance medical prudence, client communication, and evidence-based progression.
What Most Experts Agree On
Regardless of GP vs specialist, most would agree:
- A Grade 2 murmur should not be ignored
- An echo is the only way to know the cause
- No meds are started just because a murmur exists
- Prognosis is often excellent if asymptomatic
Most would agree at a minimum:
Get an echocardiogram if the dog is adult, large breed, predisposed, or if you or the owner want clarity—
But let’s dig in deeper…
The Foundation: Document and Reassess—But Don’t Stop There
Document and monitor at future visits
For many dogs, especially young or otherwise healthy individuals, a soft grade II murmur may represent a benign or physiologic finding. Careful documentation—including murmur timing, point of maximal intensity, and any concurrent findings—is essential. Serial auscultation allows the clinician to assess for progression in intensity or character over time.
However, while documentation and monitoring are appropriate initial actions, they should not be viewed as definitive management. Studies consistently show that auscultation alone has limited sensitivity and specificity for distinguishing innocent murmurs from early structural heart disease. Monitoring without a diagnostic plan risks delayed diagnosis in dogs with occult disease, particularly myxomatous mitral valve disease (MMVD), which may be clinically silent in early stages.
Diagnostics: When and Why to Go Further
Baseline diagnostics
At the first detection of a murmur, baseline diagnostics can be valuable, especially in adult or senior dogs. Thoracic radiographs and blood pressure assessment provide useful contextual information, though they cannot definitively characterize valvular disease in early stages. These tests are most helpful for establishing a baseline rather than making a diagnosis.
In-house imaging
Focused cardiac ultrasound performed by a trained clinician can offer preliminary insight into chamber size and gross valvular changes. While this may help guide next steps, it should not be considered equivalent to a comprehensive echocardiogram. In-house imaging is best viewed as a screening adjunct, not a replacement for formal cardiology assessment.
A Veterinary Cardiologist’s approach is typically more definitive:
“A murmur is not a diagnosis. The only way to know what it means is to image the heart.”
Cardiologists focus on identifying the underlying cause early, even before symptoms develop.
The Gold Standard: Echocardiography
Echocardiogram (in-house or referral)
Echocardiography remains the gold standard for evaluating heart murmurs. In an asymptomatic dog with a grade II murmur, an echocardiogram allows clinicians to:
- Confirm or rule out structural heart disease
- Identify early MMVD or congenital abnormalities
- Establish disease stage and prognosis
- Create an informed monitoring plan
Current consensus guidelines emphasize that early identification of structural disease enables appropriate surveillance and, in select cases, earlier therapeutic planning. Importantly, echocardiography also provides reassurance when no clinically relevant disease is present—benefiting both clinician confidence and client peace of mind.
Referral for echocardiography is particularly recommended when:
- The dog is middle-aged or older
- The murmur is left apical systolic
- The breed is predisposed to MMVD
- The owner seeks clarity rather than prolonged uncertainty
Clinical Takeaway: A Stepwise, Evidence-Based Approach
When I detect a grade II murmur in an otherwise asymptomatic dog, my approach is intentionally measured:
- Document thoroughly and communicate clearly with the owner.
- Assess signalment and risk factors that increase the likelihood of underlying disease.
- Pursue echocardiography—either in-house or via referral—when appropriate, recognizing it as the most definitive diagnostic step.
- Use the findings to guide monitoring frequency, client education, and long-term planning.
This approach respects the reality that not every murmur requires immediate intervention, but every murmur deserves thoughtful evaluation. Early clarity—whether confirming benignity or identifying early disease—ultimately leads to better outcomes and stronger client trust.
References (MLA)
Borgarelli, Michele, et al. “ACVIM Consensus Statement: Guidelines for the Diagnosis and Treatment of Myxomatous Mitral Valve Disease in Dogs.” Journal of Veterinary Internal Medicine, vol. 34, no. 4, 2020, pp. 1–24.
Bonagura, John D., et al. “Canine Degenerative Mitral Valve Disease: Natural History, Clinical Presentation, and Therapy.” Veterinary Clinics of North America: Small Animal Practice, vol. 45, no. 3, 2015, pp. 601–625.
Rishniw, Mark, et al. “Accuracy of Cardiac Auscultation in Detection of Canine Heart Disease.” Journal of Veterinary Internal Medicine, vol. 20, no. 3, 2006, pp. 539–546.
Häggström, Jens, et al. “Heart Murmurs in Dogs: When to Investigate Further.” Journal of Small Animal Practice, vol. 58, no. 7, 2017, pp. 375–382.