Objectives: To investigate the dependence of echocardiographic ratio indices (ERIs) on age, body weight (BW) and breed/study group using individually contributed and published summarized data in dogs. Background: ERIs allow for narrow prediction intervals of M-mode echocardiographic measurements in generic adult dogs. Breed and age-specific differences have not been examined systematically using ERI methods. Animals, materials and methods: Individual M-mode measurements were contributed by 15 published investigators from 661 dogs, allowing direct calculation of ERIs and summary statistics for each of these breed/study groups. M-mode ERI summary statistics were estimated from published summaries of 22 additional groups that included 527 adult and 36 growing dogs. Individual two-dimensional (2DE) left atrial (LA) and aortic root (Ao) measurements were contributed from 36 dogs. ERIs were analyzed for dependence on BW, breed/study group and age. Results: The majority of variation among ERIs was due to differences in the breed or study technique with comparatively little dependence on BW. Age dependence of ERIs was seen in the early growth phases of young dogs, but expected values for each ERI became static long before maturity, roughly at 10e12 weeks of age. ERIs derived from individual 2DE LA and Ao measurements showed no significant dependence on BW.