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Background: Progression to combined post‐ and pre‐capillary pulmonary hypertension (PH) provides prognostic information in human patients with post‐capillary PH. Pulmonary vascular resistance estimated by echocardiography (PVRecho) is useful for the stratification of dogs with myxomatous mitral valve disease (MMVD) and detectable tricuspid regurgitation. Objectives: To evaluate the prognostic value of PVRecho in dogs with MMVD. Animals: Fifty‐four dogs with MMVD and detectable tricuspid regurgitation. Methods: Prospective cohort study. All dogs underwent echocardiography. The PVRecho was calculated based on tricuspid regurgitation and the velocity‐time integral of the pulmonary artery flow. To evaluate the influence of echocardiographic variables on cardiac‐related deaths, Cox proportional hazard analysis was performed. Additionally, Kaplan‐Meier curves classified by PVRecho tertiles were made and compared using log‐rank tests to evaluate the influence of PVRecho on all‐cause mortality and cardiac‐related death. Results: The median follow‐up time was 579 days. Forty‐one dogs with MMVD (PH severity [number]: no or mild, 21/33; moderate, 11/11; severe, 9/10) died during the study. In the multivariable Cox proportional hazard analysis adjusted for age, sildenafil administration, and American College of Veterinary Internal Medicine stage of MMVD, left atrial to aortic diameter ratio and PVRecho remained significant (adjusted hazard ratio [95% confidence interval]: 1.2 [1.1‐1.3] and 2.1 [1.6‐3.0], respectively). Higher PVRecho showed a significant association with lower survival rates. Conclusions and Clinical Importance: Left atrial enlargement and high PVRecho were independent prognostic factors in dogs with MMVD and detectable tricuspid regurgitation. [ABSTRACT FROM AUTHOR]