Abstract The objective of this prospective observational study was to assess systolic arterial blood pressure (SABP) in small-breed dogs with degenerative mitral valve disease (MVD) from different International Small Animal Cardiac Health Council (ISACHC) heart failure classes. For this purpose, 103 client-owned dogs weighing <20kg (mean±standard deviation, 8.5±3.0kg; aged 9.8±2.9years) and presenting with MVD diagnosed by echo-Doppler examination were enrolled. Nineteen healthy dogs (9.9±2.3years; 8.7±4.2kg) were concurrently recruited as controls. SABP was measured in unsedated dogs using the Doppler method according to the recommendations in the American College of Veterinary Medicine consensus statement. SABP was significantly increased in dogs in ISACHC class 1 (n=53; median, interquartile range 140mmHg, 130-150mmHg) and class 2 (n=21; 140mmHg, 130-150mmHg), compared to the control group (n=19; 130mmHg, 120-140mmHg; P<0.01 and P<0.05, respectively), but remained within the reference interval (?160mmHg). Conversely, dogs in ISACHC class 3 showed a significantly lower SABP (n=29, 120mmHg, 110-130mmHg) than those from all other ISACHC classes (P<0.001) and the controls (P<0.05). Additionally, SABP<120mmHg was recorded in 13/103 dogs (13%). The 13 dogs were all ISACHC class 3 (3a or 3b) and were under medical treatment for heart failure. In conclusion, MVD was often associated with SABP values that were within the reference interval, but at its upper end. However, a significant decrease in SABP was observed in dogs with ISACHC heart failure class 3. Whether such low SABP values resulted from an MVD-related decrease in cardiac output, an afterload reduction owing to cardiac treatment, or both, remains to be determined.