Study expands breed-specific heart radiograph benchmarks in dogs
Bottom line
A new American Journal of Veterinary Research study adds breed-specific vertebral heart size, or VHS, and vertebral left atrial size, or VLAS, reference intervals for eight dog breeds: Australian Cattle Dogs, Shih Tzus, Maltese, Dachshunds, Greyhounds, French Bulldogs, Norwich Terriers, and Brittany Spaniels. The study included dogs with 2- or 3-view thoracic radiographs and no cardiopulmonary or systemic disease, with all measurements performed by the same board-certified cardiologist. The work builds on a growing push toward breed-adjusted radiographic interpretation, rather than relying on a single canine cutoff, because prior research has shown that thoracic conformation can shift what “normal” looks like across breeds. (pdfs.semanticscholar.org)
Why it matters: For general practitioners, emergency clinicians, radiologists, and cardiologists, the practical takeaway is straightforward: a radiographic heart that looks enlarged by a generic standard may be normal for that breed, while true enlargement could be missed if breed effects aren’t considered. That matters most in dogs being screened or monitored for conditions such as myxomatous mitral valve disease, where thoracic radiography remains widely used because it’s accessible, fast, and useful alongside exam findings and echocardiography. Recent expert commentary has also emphasized that VHS and VLAS should be measured routinely, not judged by eye alone, and interpreted in clinical context. (pubmed.ncbi.nlm.nih.gov)
What to watch: Expect more AJVR and telemedicine-based reference interval studies in additional breeds, as larger datasets continue to refine what normal cardiac silhouette measurements should be in everyday practice. (pdfs.semanticscholar.org)
Key facts
- Study
- American Journal of Veterinary Research study
- Measures
- Breed-specific vertebral heart size (VHS) and vertebral left atrial size (VLAS) reference intervals
- Breeds studied
- Australian Cattle Dogs, Shih Tzus, Maltese, Dachshunds, Greyhounds, French Bulldogs, Norwich Terriers, and Brittany Spaniels
- Study population
- Healthy dogs with 2- or 3-view thoracic radiographs
- Exclusions
- Dogs with cardiopulmonary or systemic disease
- Measurements
- All measurements were performed by the same board-certified cardiologist
- Clinical takeaway
- Generic radiographic cutoffs can misclassify normal dogs as abnormal, or obscure real disease, when breed conformation shifts baseline measurements
- Use case
- Relevant for screening or monitoring dogs for myxomatous mitral valve disease
Breed-specific cardiac radiograph benchmarks keep expanding, and the latest addition is an AJVR study establishing VHS and VLAS reference intervals for eight canine breeds: Australian Cattle Dogs, Shih Tzus, Maltese, Dachshunds, Greyhounds, French Bulldogs, Norwich Terriers, and Brittany Spaniels. The study’s premise is simple but clinically important: one-size-fits-all radiographic cutoffs can misclassify normal dogs as abnormal, or obscure real disease, when breed conformation shifts baseline heart and left atrial measurements. (pubmed.ncbi.nlm.nih.gov)
That concern isn’t new. The original vertebral heart size method was designed as a practical, reproducible way to estimate canine heart size on thoracic radiographs, but later studies found that many breeds fall outside the classic generalized reference range. Over time, published work has identified breed-specific differences in breeds including Dachshunds, Maltese, Norwich Terriers, Brittany Spaniels, Chihuahuas, Pugs, Cavalier King Charles Spaniels, and others, helping explain why a generic threshold can be misleading in practice. (pdfs.semanticscholar.org)
In the new study, investigators evaluated healthy dogs from eight breeds using 2- or 3-view thoracic radiographs and excluded dogs with cardiopulmonary or systemic disease. As in other recent AJVR reference interval studies from this research group, a single board-certified cardiologist performed the measurements, which helps reduce observer-related variability. That design mirrors a broader recent effort to generate larger, cleaner breed-specific datasets, including 2025 AJVR work in Shetland Sheepdogs, Cairn Terriers, Italian Greyhounds, and English Springer Spaniels, and 2025 AJVR work reanalyzing Yorkshire Terriers, Pomeranians, Pugs, and Boston Terriers with larger case numbers. (pubmed.ncbi.nlm.nih.gov)
The wider literature supports why both measures matter. VHS remains the most established radiographic measurement for overall cardiac size, while VLAS offers a more left-heart-focused assessment that can be especially relevant in dogs with suspected left atrial enlargement. A 2020 reference interval study in healthy adult dogs reported a median VLAS of 1.9 with a reference interval of 1.4 to 2.2 vertebrae, but later breed-specific work has shown that normal values can vary meaningfully by breed. A recent literature review also concluded that radiographic heart measurements remain important in canine cardiology, especially when paired with other diagnostic tools rather than used in isolation. (pubmed.ncbi.nlm.nih.gov)
Expert commentary in practice settings points the same way. In a 2025 dvm360 interview, Colorado State cardiologist Lance Visser said heart size assessment on thoracic radiographs “should definitely involve measurements” and described VHS and VLAS as the two primary metrics with the strongest literature support, while noting that VLAS is more specific to left heart size. That doesn’t make radiographs a substitute for echocardiography, but it reinforces their ongoing value in first-line workups, serial monitoring, and settings where echo isn’t immediately available. (dvm360.com)
Why it matters: For veterinary professionals, this is less about adding another paper to the pile and more about sharpening day-to-day decision-making. Breed-specific intervals can improve confidence when interpreting thoracic radiographs, reduce over-calling cardiomegaly in breeds with naturally higher measurements, and flag patients that need follow-up sooner. That’s especially relevant in primary care and emergency settings, where radiographs are often the first imaging step, and in conversations with pet parents weighing whether referral echocardiography is needed. (pubmed.ncbi.nlm.nih.gov)
There’s also a quality-of-evidence angle here. Recent AJVR studies from this group have leaned on large telemedicine image archives, which may help address a longstanding weakness in breed-specific reference work: small sample sizes. One 2025 AJVR paper explicitly noted that many earlier breed-specific VHS studies were based on limited populations and referenced ASVCP guidance recommending more than 120 subjects when deriving reference intervals. If that approach continues, clinicians may start to see more robust, more standardized breed-level benchmarks over the next few years. (pdfs.semanticscholar.org)
What to watch: The next step is likely continued expansion into additional breeds, plus more work linking breed-specific radiographic cutoffs to clinically meaningful outcomes, such as when to suspect preclinical myxomatous mitral valve disease, when to recommend echocardiography, and how best to track progression over time. (pubmed.ncbi.nlm.nih.gov)