BACKGROUND Obesity is a risk factor for cardiovascular disease in people, but overweight and obese human heart failure patients have improved survival compared with normal--or underweight controls--the obesity paradox. The purpose of this study was to determine if there is an association of body weight and body condition with survival in dogs with heart failure. HYPOTHESIS That body condition and changes in body weight are predictors of survival in dogs with heart failure. ANIMALS One hundred and eight dogs with heart failure (International Small Animal Cardiac Health Council stages 2, 3a, or 3b) secondary to dilated cardiomyopathy or chronic valvular disease. METHODS Medical records were reviewed, and data regarding initial body weight and body condition score (BCS), subsequent changes in body weight, and treatment were collected. Survival times were determined for dogs that were discharged from the hospital and lived >24 hours. RESULTS Survival was significantly different between dogs that gained, lost, or maintained body weight over the course of their disease (P= .04), with dogs that gained weight surviving the longest. BCS and medications were not significantly associated with survival time; however, n-3 fatty acid intake was associated with longer survival time (P= .009). CONCLUSIONS AND CLINICAL IMPORTANCE These results suggest that changes in body weight might be an important consideration in the survival of dogs with heart failure.