Radiographic Signs of Canine Cardiac Disease: VHS, VLAS, and When to Use Echocardiography

Introduction

Thoracic radiography remains the first-line imaging modality for evaluating canine cardiac disease in veterinary practice. Clinical signs such as coughing, exercise intolerance, tachypnea, or a newly detected murmur often prompt thoracic radiographs, which may reveal cardiac enlargement (cardiomegaly) or pulmonary changes consistent with congestive heart failure.

Before vertebral measurements such as VHS and VLAS are applied, thoracic radiographs should first be assessed as a whole. A structured visual review of the cardiac silhouette, trachea, great vessels, and pulmonary vasculature often reveals important clues to chamber enlargement and cardiac disease, even before formal measurements are made. This is especially useful in general practice, where the first question is often not the exact number, but whether the heart looks normal, mildly enlarged, or clearly abnormal.

In some cases, cardiac disease is identified incidentally during imaging performed for unrelated reasons such as trauma or pre-anesthetic screening.

Interpreting thoracic radiographs requires a structured approach. Radiographs can demonstrate overall heart size, chamber enlargement patterns, pulmonary vascular changes, and evidence of pulmonary edema or pleural effusion. However, they cannot assess cardiac function, which requires echocardiography.

This article focuses on how to interpret thoracic radiographs in dogs with suspected heart disease, including vertebral heart score (VHS), vertebral left atrial size (VLAS), pulmonary patterns, and when echocardiography is required for definitive diagnosis.

Accurate interpretation of cardiac disease on thoracic radiographs depends on a solid understanding of normal cardiac anatomy. Recognizing the expected position and contour of the cardiac chambers and great vessels allows clinicians to identify subtle deviations that indicate underlying disease. Without this foundation, early or mild abnormalities—particularly chamber-specific enlargement, can be easily overlooked.

Cardiac Enlargement on Radiographs

Recognizing an enlarged heart in dogs is the first step in diagnosing cardiac disease.

Radiographic assessment includes:

• Cardiac silhouette size
  
• Shape and contour
  
• Chamber-specific enlargement
  

Cardiomegaly may reflect:

• Mitral valve disease
  
• Dilated cardiomyopathy
  
• Pericardial effusion

Radiographs can allow differentiation between mild enlargement and advanced disease, especially when pulmonary edema is present.

Even before formal measurements are made, radiographs can provide useful evidence of chamber enlargement through contour changes, tracheal displacement, and focal bulging in expected chamber locations. These visual findings are often what first raise suspicion, while VHS and VLAS help quantify the impression and support serial monitoring over time.

Radiographic Patterns: MVD vs DCM vs Pericardial Effusion

Mitral Valve Disease (MVD)

• Left atrial enlargement
  
• Left ventricular enlargement
  

Dilated Cardiomyopathy (DCM)

• Generalized cardiomegaly 
• Chamber specific enlargement (specifically left atrial enlargement) can also be seen 
• In severe cases this can appear globoid
  

Pericardial Effusion

• Globoid “basketball heart” / Rounded heart on all images

Evaluating the Canine Heart on Radiographs Before VHS and VLAS

Thoracic radiographs should never be reduced to measurement alone. Before calculating VHS or VLAS, the cardiac silhouette should be assessed visually using a consistent approach. This allows identification of chamber enlargement, contour abnormalities, and secondary signs of cardiac disease that often provide the first indication of pathology.

A practical visual assessment includes:

• Overall cardiac silhouette size
• Shape and contour of the heart
• Tracheal position
• Left atrial region
• Great vessels
• Pulmonary vessels and lung pattern

Findings that may help localize chamber enlargement:

Left-sided enlargement

• Straightening of caudal cardiac border
• Dorsal tracheal deviation
• Increased opacity in the region of the left atrium
• Left auricular bulge (VD/DV)

Right-sided enlargement

• Increased sternal contact
• Rounding of cranial cardiac border
• Broadening of the right heart margin

These subjective findings are often apparent before measurements are performed and should guide interpretation. VHS and VLAS provide objective support but should not replace visual assessment.

Measuring Vertebral Heart Score (VHS)

The canine vertebral heart score is a  widely used method to quantify cardiac size on radiographs, and can be used to monitor changes in cardiovascular structures over time, helping assess progression of heart disease.

Step-by-Step VHS Measurement

1. Obtain a  well collimated and well positioned right lateral thoracic radiograph. Significant obliquity of the radiograph can substantially affect the accuracy of this measurement.
   
2. Measure the long axis:
   
   • From base of the carina to cardiac apex
     
3. Measure the short axis:
   
   • Perpendicular to long axis at widest point
     
4. Transfer both measurements to vertebrae starting at T4
   
5. Add values
   

Final value = vertebral heart score (VHS)

Normal VHS Ranges

• Dogs: 8.7–10.7 vertebrae
  
• Mean: ~9.7
  
• 10.7 → cardiomegaly

Breed Variation

Studies show a significantly higher VHS in toy and brachiocephalic breeds risking over diagnosis if standard references are used. 

Breed Variation in Canine Vertebral Heart Score (VHS)

Breed	Mean VHS (± SD)	Comparison to Standard (9.7 ± 0.5)	Clinical Note	Reference
Mixed breed (reference)	9.7 ± 0.5	Baseline	Original reference population	Buchanan & Bücheler, 1995
Pug	~10.5–11.0	↑ Higher	Risk of false positive cardiomegaly	Lamb et al., 2001; Jepsen-Grant et al., 2013
English Bulldog	~10.5–11.0	↑ Higher	Vertebral anomalies common	Lamb et al., 2001
Boston Terrier	~10.3–10.8	↑ Higher	Brachycephalic conformation	Lamb et al., 2001
Pomeranian	~10.7 ± 0.6	↑ Higher	Toy breed variation	Kim et al., 2018
Toy Poodle	~9.9 ± 0.6	Slightly ↑	Overlaps normal range	Kim et al., 2018
Brittany Spaniel	~10.6 ± 0.2	↑ Higher	Breed-specific reference recommended	Bavegems et al., 2005
Dachshund	~9.5–10.0	Variable	Influenced by body condition	Jepsen-Grant et al., 2013
Beagle	~10.0–10.5	↑ Slightly higher	Mild upward shift	Gugjoo et al., 2013

Common Errors

Overestimation:

• Oblique positioning
• Including fat or fluid
• Incorrect axis placement
• Cardiac cycle
• Variation in measurements between readers
• Variation in vertebra size (hemivertebra)
  

Underestimation:

• Poor inspiration
• Incorrect T4 identification
• Does not directly include the left atrium
  

CAUTION:

As discussed above, numerous factors can influence VHS measurements, and the wide variation reported in the normal range limits its consistency and reliability. Therefore, VHS should not be used as the sole metric to determine cardiac enlargement.

VLAS — Assessing Left Atrial Enlargement

The vertebral left atrial size (VLAS) is used to help detect left atrial enlargement in dogs, 

1. How to Measure VLAS (VLAS Measurement Technique)
2. View: Use a right or left lateral thoracic radiograph (centered on the heart).
3. Measure: Start at the center of the ventral margin of the carina and extend the line to the caudal edge of the left atrium, where it intersects the dorsal border of the caudal vena cava.
4. Transfer to vertebrae starting at T4
   
5. Record value
   

Normal Values

• Normal: 1.4–2.2 v
  
• 2.3 v → enlargement

Breed Variation 

Breeds with Higher or Wider VLAS Ranges

Breed	VLAS (Mean ± SD / Range)	Type of Variation	Reference
Pomeranian	2.17 ± 0.26	↑ Higher mean + wider spread	Kim JH et al. (2018).
Toy Poodle	2.02 ± 0.15	↑ Slightly higher mean	Kim JH et al. (2018).
Maltese	2.03 ± 0.17 (IQR ~1.8–2.1)	↑ Slightly higher mean	Kim JH et al. (2018);
Chihuahua	~1.8 ± 0.2 (range ~1.3–2.1)	Wider range	Hezzell MJ et al. (2020).
Miniature Australian Shepherd	~1.7–2.5	↑ Wider range (higher upper limit)	Baisan RA et al. (2025).
American Eskimo	~1.7–2.4	↑ Wider range	Baisan RA et al. (2025).
Tibetan Terrier	~1.7–2.3	Slightly wider range	Baisan RA et al. (2025).
Border Terrier	~1.7–2.3	Slightly wider range	Baisan RA et al. (2025).

Clinical Relevance

VLAS is a useful tool when evaluating and monitoring mitral valve disease:

• Early enlargement → monitoring: by repeating radiographs in 9-12 months.
  
• Significant enlargement → consider treatment
  

Pulmonary Changes in Cardiac Disease

Radiographs are essential for detecting pulmonary edema in dogs and CHF.

Pulmonary Venous Congestion

• Typically done by comparing the diameter of the pulmonary veins to the accompanying arteries and adjacent ribs (4th rib on lateral radiographs and 9th on VD image
• Veins larger than accompanying artery are suggestive of venous congestion
• Veins larger to their adjacent ribs at the point of intersection with these ribs are suggestive of venous congestion
• Both arteries and veins can be enlarged together suggestive of volume overload/congestion
  

Pulmonary Edema

• Interstitial pattern which can coalesce into an alveolar pattern
  
• Perihilar and caudodorsal distribution in dogs (feline patients can have a more random distribution)
  

Progression

Normal → congestion → interstitial → alveolar

When Radiographs Are Enough vs When Echocardiography Is Required

Radiographs are useful for:

• Identifying moderate to severe enlarged heart in dogs
• Detecting pulmonary edema
• Monitoring response to treatment of CHF
• Monitor progression of known cardiac disease
  

Echocardiography is required for:

• Valve assessment
• Cardiac function
• Definitive diagnosis
• Evaluating for comorbidities such as pulmonary hypertension, cardiac mass and thrombi
• Fever of unknown origin
  

AI-Assisted VHS and VLAS Measurement

Measuring VHS and VLAS manually can introduce variability between clinicians.

AI-assisted tools can:

• Automatically calculate VHS and VLAS
  
• Standardize cardiac measurements

SignalPET helps clinicians evaluate thoracic radiographs more consistently, reducing variability between readers

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