Objective: To evaluate serial changes in echocardiography and cardiac biomarkers in dogs with suspected diet-associated DCM, after diet change. Dogs with DCM [M-mode fractional shortening (FS) ≤ 25%, normalized LVIDd ≥1.8, and normalized LVIDs (nLVIDs) ≥ 1.2] eating either a non-traditional or traditional diet were enrolled in a 9-month study. Echocardiography, ECG, high-sensitivity cardiac troponin I (cTnI), NT-proBNP, and taurine were measured at baseline. Dogs were treated with cardiac medications as clinically indicated, diet was changed, and echocardiography and biomarker analyses were repeated after 3, 6, and 9 months. As of January, 2020, 59 dogs have been enrolled (36 M/23 F). Median age = 7.7 yrs (2.6-15.9 yrs) and weight was 32.0 kg (3.8-97.8 kg). Enrolled breeds included Doberman Pinscher (n=14), Golden Retriever (n=7), Pit Bull (n=6), and Boxer (n=6), but multiple other breeds were represented. Dogs were ACVIM Stage C (n=45) or Stage B (n=14). Fifty-one of 59 dogs (86.4%) were eating non-traditional diets. Six of 59 dogs had mildly reduced plasma (n=3) or whole blood (n=3) taurine concentrations. To date, 41 of 42 dogs still alive were re-evaluated at 3 months (23 at 6 months, 16 at 9 months). At 3 months, dogs originally eating non-traditional diets had increased FS (P < 0.001) and decreased nLVIDs (P = 0.003), left atrium:aorta (P = 0.002), NT-proBNP (P = 0.04), and cTnI (P = 0.003) compared to baseline. 3/9 traditional diet dogs were alive at 3 months. Overall, 27 dogs died or were euthanized [12/27 (44.4%) due to sudden death].