BACKGROUND: Reduction in 30-day readmission rates following hospitalization for acute coronary syndrome (ACS) and acute decompensated heart failure (ADHF) is a national goal. OBJECTIVE: The aim of this study was to determine the effect of a tailored, pharmacist-delivered, health literacy intervention on unplanned health care utilization, including hospital readmission or emergency room (ER) visit, following discharge. DESIGN: Randomized, controlled trial with concealed allocation and blinded outcome assessors SETTING: Two tertiary care academic medical centers PARTICIPANTS: Adults hospitalized with a diagnosis of ACS and/or ADHF INTERVENTION: Pharmacist-assisted medication reconciliation, inpatient pharmacist counseling, low-literacy adherence aids, and individualized telephone follow-up after discharge MAIN MEASURES: The primary outcome was time to first unplanned health care event, defined as hospital readmission or an ER visit within 30 days of discharge. Prespecified analyses were conducted to evaluate the effects of the intervention by academic site, health literacy status (inadequate versus adequate), and cognition (impaired versus not impaired). Adjusted hazard ratios (aHR) and 95 % confidence intervals (CI) are reported. KEY RESULTS: A total of 851 participants enrolled in the study at Vanderbilt University Hospital (VUH) and Brigham and Women's Hospital (BWH). The primary analysis showed no statistically significant effect on time to first unplanned hospital readmission or ER visit among patients who received interventions compared to controls (aHR = 1.04, 95 % CI 0.78-1.39). There was an interaction of treatment effect by site (p = 0.04 for interaction); VUH aHR = 0.77, 95 % CI 0.51-1.15; BWH aHR = 1.44 (95 % CI 0.95-2.12). The intervention reduced early unplanned health care utilization among patients with inadequate health literacy (aHR 0.41, 95 % CI 0.17-1.00). There was no difference in treatment effect by patient cognition. CONCLUSION: A tailored, pharmacist-delivered health literacy-sensitive intervention did not reduce postdischarge unplanned health care utilization overall. The intervention was effective among patients with inadequate health literacy, suggesting that targeted practice of pharmacist intervention in this population may be advantageous.