Measurement example of VLAS. The Vertebral Left Atrial Size (VLAS) measurement in the same right lateral thoracic radiograph is shown in Figure 1. A line was drawn from the ventral margin of the carina tracheae to the dorsal intersection between the cardiac silhouette and the caudal vena cava (red line on cardiac silhouette). This line was transposed onto the vertebral column (red line on vertebral) as described in Figure 1. The VLAS was 2.2 vertebral units.