SABP was significantly increased in dogs in ISACHC class 1 (n = 53; median, interquartile range 140 mmHg, 130-150 mmHg) and class 2 (n = 21; 140 mmHg, 130-150 mmHg), compared to the control group (n = 19; 130 mmHg, 120-140 mmHg; P < 0.01 and P < 0.05, respectively), but remained within the reference interval (?160 mmHg). Conversely, dogs in ISACHC class 3 showed a significantly lower SABP (n = 29, 120 mmHg, 110-130 mmHg) than those from all other ISACHC classes (P < 0.001) and the controls (P < 0.05). Additionally, SABP < 120 mmHg 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.