In this study, the authors describe the temporal changes in clinical and radiographic variables prior to development of congestive heart failure (CHF) in dogs with stage B2 myxomatous mitral valve disease. Dogs developing CHF showed increased heart rates, respiratory rates at home and in the clinic, and vertebral heart sums. Rectal temperatures and body weights were decreased. Vertebral heart sums gradually increased over 12 months, whereas the other variables changed in the 2 to 10 months prior to developing CHF. The variables with the highest absolute change and rate of change were observed with respiratory rates at home and in the clinic, suggesting monitoring of these variables may enable earlier detection and management of CHF.