• Using a lateral thoracic radiograph, ensure the thoracic vertebrae T4 to T12 are clearly delineated.
• Measurements can also be taken on ventrodorsal (VD) or dorsoventral (DV) projections, but this measurement is not as consistent between animals. Measurement from a lateral projection is recommended.
• Using calipers, measure the longest axis of the cardiac silhouette from the carina of the mainstem bronchus to the apex (designated “L”, "Long Axis")
• Transfer this long axis measurement to the vertebrae, starting at the cranial edge of T4, and count the number of vertebrae that fall within the caliper points
• Using calipers, measure the short axis at the widest part of the cardiac silhouette, perpendicular to the long axis measurement (designated “S”, "Short Axis")
• Transfer this short axis measurement to the vertebrae, starting at the cranial edge of T4, and count the number of vertebrae that fall within the caliper points
• Add the two measurements.

VHS = L + S

Buchanan JW, Bucheler J. Vertebral scale system to measure canine heart size in radiographs. JAVMA. 1995;206(2):194–199.

• The published range for a normal VHS is 9.2-10.3 on a lateral radiograph, with 10.5 suggested as the cutoff for of cardiomegaly in adult dogs
• The reference values for vertebral heart scale measured on VD and DV radiographs are 9.4-11.0 and 8.8-11.7, respectively, for dogs
• The boxer, bulldog (French and English), Boston terrier, Cavalier King Charles spaniel, Labrador retriever, pug, Pomeranian, and whippet have been found to have average values that are much higher than other dog breeds.

  VHS Breed Chart

• A normal range of 6.7-8.1 has been established for cats.