Vertebral scale system to measure heart size in radiographs.

This article describes a method for measuring heart size relative to vertebral length in radiographs. The lengths of the long and short axes of the heart are scaled against the length of vertebrae dorsal to the heart beginning with the fourth thoracic vertebra (v). The sum of the long and short axes of the heart is the vertebral heart size (VHS). In 100 normal dogs, VHS was 9.7 v +/- 0.5 SD. The differences between wide- and deep-chested dogs, males and females, and right or left lateral recumbency were not significant. In 100 normal cats, the average VHS was 7.5 v +/- 0.3. The short-axis dimension of the heart in ventrodorsal radiographs of cats was 3.4 v +/- 0.25.