1. Introduction
The Maltese is one of the most recognizable and beloved toy breeds worldwide, known for its long, silky white coat, compact size, and affectionate temperament. Typically weighing between 2–4 kg, Maltese dogs are often considered ideal companions for apartment living and owners seeking a small, people-oriented pet. However, like many toy breeds, their small stature comes with unique health considerations—particularly in relation to cardiovascular disease. Accurate cardiac assessment is therefore a critical component of routine veterinary care for this breed.
Heart disease is a common concern in toy breeds, with degenerative valvular conditions such as myxomatous mitral valve disease (MMVD) occurring with high prevalence as dogs age. Because the Maltese often live well into their teens, cumulative cardiovascular changes are frequently encountered in clinical practice. Early identification of cardiac enlargement and disease progression is essential for timely intervention, therapeutic planning, and client education. Thoracic radiography remains one of the most accessible and widely used diagnostic tools for cardiac evaluation in general practice.
Two radiographic measurements are particularly valuable for objective assessment: the Vertebral Heart Score (VHS) and the Vertebral Left Atrial Size (VLAS). While general reference ranges exist, breed-specific variations are well documented, and applying inappropriate cutoffs can lead to over- or under-diagnosis. Fortunately, the Maltese is one of the toy breeds whose cardiac silhouette closely aligns with general canine reference values, making interpretation somewhat more straightforward than in breeds with marked anatomical deviations.
Despite this advantage, challenges remain. The Maltese’s small thoracic size, potential for positioning artifacts, and higher likelihood of concurrent conditions (such as tracheal collapse or hepatic shunts) can complicate radiographic interpretation. This guide provides a comprehensive, breed-specific overview of VHS and VLAS reference values in the Maltese, discusses common cardiac diseases affecting the breed, and offers practical guidance for measurement, monitoring, and clinical decision-making. It is designed as a practical reference for veterinarians seeking to optimize cardiac assessment in this popular toy breed.
2. Maltese VHS Reference Values
The Vertebral Heart Score (VHS) is a standardized radiographic method for assessing cardiac size on lateral thoracic radiographs. By comparing the long and short axes of the heart to the length of thoracic vertebrae starting at T4, VHS provides an objective, reproducible estimate of overall heart size that reduces subjectivity compared to visual assessment alone. In the Maltese, VHS interpretation is generally reliable and closely aligned with established canine norms.
Normal VHS for the Maltese
Current breed-specific data indicate that the normal VHS for the Maltese is 9.53 ± 0.46 vertebrae (v). This value is very close to the classic general canine reference range, which is often cited as approximately 9.7 ± 0.5 v. The relatively small deviation highlights an important clinical advantage: the Maltese is a toy breed for which general VHS cutoffs are usually appropriate.
The 95% reference range for Maltese VHS is approximately 8.6–10.5 v, encompassing the majority of clinically normal individuals. Most healthy Maltese dogs will fall squarely within this range when properly positioned and measured on high-quality right lateral thoracic radiographs.
Comparison to General Canine References
Unlike some breeds with extreme thoracic conformation—such as Bulldogs, Dachshunds, or deep-chested sighthounds—the Maltese has a relatively balanced thoracic shape. As a result, its cardiac silhouette does not exhibit the marked breed-related distortion seen in those dogs. This makes the Maltese particularly well suited for the use of general VHS cutoffs, especially in general practice settings where breed-specific charts may not always be readily available.
However, it is still important to recognize that “normal” is a range rather than a single number. A Maltese with a VHS of 10.4 v may be entirely normal if asymptomatic and stable over time, whereas a dog with a VHS of 10.1 v that has increased from 9.3 v within a year may warrant closer investigation.
When to Suspect Cardiomegaly
In the Maltese, cardiomegaly should be suspected when VHS values consistently exceed 10.5 v, particularly if accompanied by clinical signs such as coughing, exercise intolerance, or a newly detected heart murmur. Progressive increases in VHS over serial radiographs are often more clinically meaningful than a single measurement taken in isolation.
It is also important to interpret VHS in conjunction with other findings, including:
- Pulmonary vasculature size
- Evidence of pulmonary edema
- Tracheal elevation
- Left atrial enlargement (best assessed with VLAS)
In early MMVD, VHS may remain within the upper end of normal while subtle left atrial enlargement is already present. Therefore, while the Maltese is a good candidate for general VHS interpretation, VHS should never be the sole determinant of cardiac health. Instead, it should be integrated into a comprehensive diagnostic framework that includes auscultation, clinical history, and—when indicated—echocardiography.
3. Maltese VLAS Reference Values
The Vertebral Left Atrial Size (VLAS) is a radiographic measurement specifically designed to assess left atrial enlargement on lateral thoracic radiographs. Given that left atrial enlargement is a hallmark of many clinically significant cardiac diseases—particularly myxomatous mitral valve disease—VLAS has become an increasingly valuable tool in small-breed cardiology.
Normal VLAS for the Maltese
In clinically normal Maltese dogs, the median VLAS is approximately 2.0 vertebrae, with an interquartile range (IQR) of 1.8–2.1 v. This places the Maltese slightly higher than some other toy breeds but still well within the generally accepted normal range for dogs.
This mildly elevated baseline is important to recognize. A VLAS of 2.1 v in a Maltese may be completely normal, whereas the same measurement in another toy breed might raise greater suspicion for early left atrial enlargement. Breed awareness is therefore essential to avoid overinterpretation.
Comparison With Other Breeds
Some small breeds, such as Chihuahuas or Pomeranians, may have slightly lower median VLAS values, while others prone to early atrial remodeling may trend higher. The Maltese sits near the center of this spectrum. Its thoracic anatomy allows for relatively consistent visualization of the left atrium, making VLAS a particularly reliable metric when radiographs are properly obtained.
Clinical Interpretation of VLAS
In the Maltese, VLAS values above approximately 2.3–2.4 v should prompt closer evaluation, especially if accompanied by:
- A systolic heart murmur
- Increasing VHS
- Respiratory signs or cough
- Evidence of pulmonary venous congestion
VLAS is especially useful for detecting early disease progression in dogs with known MMVD. Left atrial enlargement often precedes overt clinical signs, and subtle increases in VLAS over time can help guide decisions regarding echocardiography, staging, and treatment initiation.
As with VHS, serial measurements are critical. A Maltese whose VLAS increases from 1.9 v to 2.3 v over 6–12 months may be demonstrating meaningful disease progression, even if the absolute value remains near the upper limit of normal. When used thoughtfully, VLAS provides a sensitive, accessible window into left-sided cardiac remodeling in this breed.
4. Heart Disease in Maltese
Myxomatous Mitral Valve Disease (MMVD)
Myxomatous mitral valve disease is by far the most common cardiac condition affecting Maltese dogs. As a classic toy breed, the Maltese has a high lifetime risk of developing MMVD, with prevalence increasing markedly with age. Degenerative changes of the mitral valve lead to regurgitation, progressive volume overload of the left atrium and ventricle, and eventual cardiac remodeling.
Radiographically, early MMVD may present with a normal VHS but a subtly increased VLAS. As the disease progresses, left atrial enlargement becomes more pronounced, followed by generalized cardiomegaly. Pulmonary venous congestion and edema may develop in advanced stages. VHS and VLAS together are therefore invaluable for staging and monitoring MMVD in the Maltese.
Patent Ductus Arteriosus (PDA)
Although less common than MMVD, patent ductus arteriosus is an important congenital cardiac condition occasionally diagnosed in Maltese dogs. PDA results in a left-to-right shunt, leading to volume overload of the left heart. Radiographic findings may include marked left atrial and ventricular enlargement, increased pulmonary vasculature, and a characteristic bulge in the region of the main pulmonary artery.
In young Maltese patients, unexpectedly high VHS and VLAS values—particularly in the absence of a degenerative murmur—should raise suspicion for congenital disease and prompt echocardiographic evaluation.
Portosystemic Shunts and Cardiac Assessment
Congenital portosystemic shunts (PSS) are not uncommon in Maltese dogs and can indirectly affect cardiac assessment. Dogs with PSS may have microhepatica, altered abdominal organ positioning, and systemic metabolic changes that influence thoracic appearance and cardiovascular physiology. In some cases, reduced preload may result in a deceptively small cardiac silhouette, potentially masking early cardiac disease.
Understanding the presence of concurrent systemic conditions is essential when interpreting VHS and VLAS in this breed.
Age-Related Changes
As Maltese dogs age, mild increases in VHS and VLAS may occur even in the absence of overt clinical disease. Differentiating normal aging changes from early pathology requires careful trend analysis, thorough clinical assessment, and, when appropriate, echocardiography. Age alone should never be the sole explanation for progressive cardiac enlargement.
5. Measurement Considerations
Accurate radiographic measurement in Maltese dogs requires attention to several breed-specific challenges. Their small body size means that even minor positioning errors can significantly affect VHS and VLAS values. Slight rotation, poor inspiration, or suboptimal limb positioning can artificially increase or decrease measured heart size.
High-quality radiographs are essential. Proper exposure, true lateral positioning, and consistent technique are critical for reliable serial comparisons. Because the Maltese thorax is small, magnification errors can also have a proportionally larger impact than in larger breeds.
Radiographic Quality Needs
- Right lateral views are preferred for VHS and VLAS consistency
- Full inspiration minimizes false cardiomegaly
- Clear visualization of vertebral landmarks is essential
Benefits of AI Assistance
Emerging AI-assisted radiographic analysis tools offer particular benefits in toy breeds like the Maltese. Automated vertebral identification, measurement consistency, and trend tracking can reduce interobserver variability and improve early detection of subtle changes. While AI should not replace clinical judgment, it can be a valuable adjunct in routine monitoring and busy clinical settings.
6. Monitoring Protocol
For healthy adult Maltese dogs with no murmurs, baseline thoracic radiographs in early adulthood can be valuable for future comparison. In dogs with detected heart murmurs or known MMVD, radiographic monitoring should be more structured.
Recommended Schedule
- No murmur, asymptomatic: Radiographs every 2–3 years
- Murmur present, asymptomatic: Every 12–18 months
- Known MMVD with enlargement: Every 6–12 months, or sooner if clinical signs develop
When to Escalate
Escalation to echocardiography is recommended when:
- VHS or VLAS shows progressive increase
- Values exceed breed-adjusted expectations
- Clinical signs such as cough, tachypnea, or exercise intolerance appear
Early escalation allows for accurate staging and timely therapeutic intervention.
7. Clinical Case
A 9-year-old neutered male Maltese presented for an annual wellness exam. A grade II/VI left apical systolic murmur was auscultated, but the dog was asymptomatic. Baseline thoracic radiographs revealed a VHS of 9.9 v and a VLAS of 2.2 v. While both values were near the upper end of normal, they were not definitively abnormal for the breed.
Given the patient’s age and murmur, echocardiography was recommended and confirmed early-stage MMVD with mild left atrial enlargement. No medication was initiated, but a monitoring plan was established. One year later, repeat radiographs showed a VHS of 10.4 v and a VLAS of 2.5 v, prompting initiation of therapy and closer follow-up. This case highlights the value of breed-aware interpretation and serial measurement.
8. Summary
The Maltese is a toy breed well suited to radiographic cardiac assessment using VHS and VLAS. With a normal VHS of 9.53 ± 0.46 v and a median VLAS of 2.0 v, most Maltese dogs fall close to general canine reference ranges. Understanding breed-specific nuances, common cardiac diseases, and proper measurement techniques allows veterinarians to confidently detect early disease, monitor progression, and optimize long-term cardiac care for this popular breed.
Related Resources
- Breed-Specific VHS Comparison Chart - Compare VHS and VLAS values across multiple breeds
- VHS (Vertebral Heart Score) Complete Guide - Learn the fundamentals of VHS measurement
- VLAS (Vertebral Left Atrial Size) Guide - Understanding left atrial measurements