This study aimed to establish reference values for vertebral heart size (VHS) and manubrium heart score (MHS) in healthy adult Border Collies. The study utilized 12 dogs, both male and female, aged between 1 and 9 years. All dogs exhibited normal results on B- and M-mode echocardiography. Thoracic radiographs were taken in left lateral (LL), right lateral (RL), and ventrodorsal (VD) recumbency. Both subjective and objective analyses were conducted by two evaluators. The reproducibility of the objective radiographic measurements was excellent (P < 0.001), with the following mean values and standard deviations: VHS LL = 9.95 ± 0.47; VHS RL = 10.10 ± 0.51; VHS VD = 10.84 ± 0.61; Short-MHS RL = 2.10 ± 0.17; Long-MHS RL = 2.57 ± 0.19; Overall MHS RL = 4.65 ± 0.33; Short-MHS VD = 2.13 ± 0.22; Long-MHS VD = 2.94 ± 0.26, and Overall MHS VD = 5.03 ± 0.42. This study contributes to the standardization of VHS and MHS measurements, thereby aiding in the evaluation of the cardiac silhouette of Border Collies.