Abstract: This study aimed to estimate the prevalence of tracheobronchial collapse in dogs with Chronic Degenerative Mitral valvular Disease (CDMD) and to clarify the relationship between left atrial enlargement and airway collapse in clinically healthy small-breed dogs and dogs with CDMD at various stages of heart failure. 54 clinically healthy dogs and 133 CDMD dogs were evaluated. The angle of Tracheal Bifurcation (TB angle), luminal diameters of the trachea and bronchi, ratio of the tracheal or bronchial diameters to the thoracic inlet distance (TD/TI), diameters at 6 locations (i.e., cervical, thoracic inlet, thoracic, carina and right and left cranial lobar bronchi) and vertebral heart scale were measured on digital thoracic radiographs. The prevalence of collapsed trachea prior to carina in clinically healthy dogs and those with CDMD were 28 and 29%, respectively. Compared to healthy controls, the TB angle, TD/TI at the carina and left cranial Lobar Bronchus (LB) of the CDMD dogs that were categorized in the modified New York Heart Association functional classification 3 and 4 were significantly different. VHS in CDMD was negatively correlated to carina/TI, right cranial LB/TI and left cranial LB/TI. The left atrial diameter/aortic root diameter was negatively correlated to carina/TI, right cranial LB and left cranial LB/TI. The results indicated that a collapsed trachea was not associated with CDMD in dogs. The narrowing of the trachea and bronchus in CDMD dogs developed where the anatomical regions were in direct contact with the left atrium. The degree of tracheobronchial compression was associated with the severity of CDMD.