BACKGROUND: Limited data exist on the characterization and outcomes of cats with cardiomyopathy and benign ureteral obstruction treated by subcutaneous ureteral bypass (SUB) placement. HYPOTHESIS/OBJECTIVES: Characterize cardiomyopathies, assess perioperative and long-term outcomes, and determine if an association exists between left atrial size and fluid overload (FO) or survival. ANIMALS: Ninety-four cats presented for SUB placement between 2010 and 2022 at the Veterinary Teaching Hospital of the University of Montreal. METHODS: Retrospective review of medical records including physical examination, serum creatinine concentration, echocardiography, and outcome. Cats were grouped as: cardiomyopathy present (CM+) or absent (CM-). RESULTS: Echocardiography was performed in 64/94 (68%) cats. Cardiomyopathy was diagnosed in 26/64 (40%) cats, including 85% (22/26) hypertrophic or hypertrophic obstructive cardiomyopathy. The majority of cats (22/26) had mild cardiomyopathy, with normal left atrial size (left atrial-to-aortic root diameter ratio in right parasternal short axis [LA:AoSAX] < 1.6). No significant difference in duration of hospitalization, survival time, renal recovery, or frequency of FO was found between CM+ and CM- cats. Fluid overload occurred in 45% (29/64) of the cats, and was associated with shorter survival (median [IQR]: 430 [40; 1260] days vs 1020 [494; 1668] days; P = .005). Admission serum creatinine concentration was higher in cats with FO (mean ± SD: 11.12 ± 5.93 mg/dL vs 6.16 ± 5.44 mg/dL; P < .001) and was associated with worse prognosis (P = .01). The LA:AoSAX was not associated with FO (P = .26) or survival (P = .39). CONCLUSIONS AND CLINICAL IMPORTANCE: Mild cardiomyopathy was a common comorbidity but did not affect outcome and should not be considered a contraindication for SUB placement. However, the impact of more advanced cardiac disease remains unknown. In contrast, FO and higher serum creatinine concentration at admission predicted shorter survival.