We examined whether an additive treatment with an angiotensin receptor blocker, olmesartan, reduces the mortality and morbidity in hypertensive patients with chronic heart failure (CHF) treated with angiotensin-converting enzyme (ACE) inhibitors, β-blockers, or both. In this prospective, randomized, open-label, blinded endpoint study, a total of 1147 hypertensive patients with symptomatic CHF (mean age 66 years, 75% male) were randomized to the addition of olmesartan (n = 578) to baseline therapy vs. control (n = 569). The primary endpoint was a composite of all-cause death, non-fatal acute myocardial infarction, non-fatal stroke, and hospitalization for worsening heart failure. During a median follow-up of 4.4 years, the primary endpoint occurred in 192 patients (33.2%) in the olmesartan group and in 166 patients (29.2%) in the control group [hazard ratio (HR) 1.18; 95% confidence interval (CI), 0.96–1.46, P = 0.112], while renal dysfunction developed more frequently in the olmesartan group (16.8 vs. 10.7%, HR 1.64; 95% CI 1.19–2.26, P = 0.003). Subgroup analysis revealed that addition of olmesartan to combination of ACE inhibitors and β-blockers was associated with increased incidence of the primary endpoint (38.1 vs. 28.2%, HR 1.47; 95% CI 1.11–1.95, P = 0.006), all-cause death (19.4 vs. 13.5%, HR 1.50; 95% CI 1.01–2.23, P = 0.046), and renal dysfunction (21.1 vs. 12.5%, HR 1.85; 95% CI 1.24–2.76, P = 0.003). Additive use of olmesartan did not improve clinical outcomes but worsened renal function in hypertensive CHF patients treated with evidence-based medications. Particularly, the triple combination therapy with olmesartan, ACE inhibitors and β-blockers was associated with increased adverse cardiac events. This study is registered at clinicaltrials.gov-NCT00417222.