OBJECTIVES: This was a retrospective analysis to determine the effect of diabetes on outcome in patients with advanced heart failure (HF), and to determine the effect of beta-blockade in patients with HF with and without diabetes mellitus. BACKGROUND: In chronic HF the impact on clinical outcomes and therapeutic response of the prevalent comorbid condition diabetes mellitus has not been extensively investigated. METHODS: We assessed the impact of diabetes on prognosis and effectiveness of beta-blocker therapy with bucindolol in patients with HF enrolled in the Beta-Blocker Evaluation of Survival Trial (BEST). We conducted a retrospective analysis to examine the prognosis of patients with advanced HF with and without diabetes, and the effect of beta-blocker therapy on mortality and HF progression or myocardial infarction (MI). The database was the 2,708 patients with advanced HF (36% with diabetes and 64% without diabetes) who were randomized to the beta-blocker bucindolol or placebo in BEST and followed for mortality, hospitalization, and MI for an average of two years. RESULTS: Patients with diabetes had more severe chronic HF and more coronary risk factors than patients without diabetes. Diabetes was independently associated with increased mortality in patients with ischemic cardiomyopathy (adjusted hazard ratio 1.33, 95% confidence interval 1.12 to 1.58, p = 0.001), but not in those with a nonischemic etiology (adjusted hazard ratio 0.98, 95% confidence interval 0.74 to 1.30, p = 0.89). Compared with patients without diabetes, in diabetic patients beta-blocker therapy was at least as effective in reducing death or HF hospitalizations, total hospitalizations, HF hospitalizations, and MI. Ventricular function and physiologic responses to beta-blockade were similar in patients with and without diabetes. CONCLUSIONS: Diabetes worsens prognosis in patients with advanced HF, but this worsening appears to be limited to patients with ischemic cardiomyopathy. In advanced HF beta-blockade is effective in reducing major clinical end points in patients with and without diabetes.