Background: The clinical outcome of dogs affected by degenerative mitral valve disease (MVD) without overt clinical signs is still poorly defined, and criteria for identification of animals that are at a higher risk of early decompensation have not yet been determined. Hypothesis: N-terminal pro-B-type natriuretic peptide plasma concentration (NT-proBNP) is correlated with mitral regurgitation (MR) severity and can predict disease progression in dogs with asymptomatic MVD. Animals: Seventy-two dogs with asymptomatic MVD, with or without heart enlargement (International Small Animal Cardiac Health Council: ISACHC classes 1a and 1b), and a control group of 22 dogs were prospectively recruited. Methods: Severity of MR was quantitatively assessed from the regurgitation fraction (RF) by the proximal isovelocity surface area method. Consequences of MR were evaluated from measurements of the left atrium/aorta ratio (LA/Ao), fractional shortening (FS), end-diastolic and end-systolic left ventricular volumes indexed to body surface area (EDVI and ESVI). The relevance of these echo-Doppler indices and NT-proBNP for prediction of outcome at 12 months was studied. Results: A significant correlation was found between NT-proBNP and RF, LA/Ao, FS, and EDVI (P<.05). NT-proBNP was higher in dogs with MVD (ISACHC classes 1a and 1b) compared with the control group (P=.025 and <.001, respectively). The difference was not significant when only dogs from ISACHC class 1a with RF<30% were considered. Lastly, NT-proBNP was higher in dogs that underwent MVD decompensation at 12 months (P<.05). Conclusions and Clinical Importance: NT-proBNP is correlated with MVD severity and prognosis in dogs with asymptomatic MVD.