BACKGROUND Chronic angina is more common in patients with diabetes mellitus (DM) with poor glucose control. Ranolazine both treats chronic angina and improves glucose control. OBJECTIVES This study sought to examine ranolazine's antianginal effect in relation to glucose control. METHODS The authors performed a secondary analysis of the RIVER-PCI (Ranolazine in Patients with Incomplete Revascularization after Percutaneous Coronary Intervention) trial, a clinical trial in which 2,604 patients with chronic angina and incomplete revascularization following percutaneous coronary intervention were randomized to ranolazine versus placebo. Mixed-effects models were used to compare the effects of ranolazine versus placebo on glycosylated hemoglobin (HbA(1c)) at 6- and 12-month follow-up. Interaction between baseline HbA(1c) and ranolazine's effect on Seattle Angina Questionnaire angina frequency at 6 and 12 months was tested. RESULTS Overall, 961 patients (36.9%) had DM at baseline. Compared with placebo, ranolazine significantly decreased HbA(1c) by 0.42 +/- 0.08% (adjusted mean difference +/- SE) and 0.44 +/- 0.08% from baseline to 6 and 12 months, respectively, in DM patients, and by 0.19 +/- 0.02% and 0.20 +/- 0.02% at 6 and 12 months, respectively, in non-DM patients. Compared with placebo, ranolazine significantly reduced Seattle Angina Questionnaire angina frequency at 6 months among DM patients but not at 12 months. The reductions in angina frequency were numerically greater among patients with baseline HbA(1c) >= 7.5% than those with HbA(1c) <7.5% (interaction p = 0.07). CONCLUSIONS In patients with DM and chronic angina with incomplete revascularization after percutaneous coronary intervention, ranolazine's effect on glucose control and angina at 6 months was proportionate to baseline HbA(1c), but the effect on angina dissipated by 12 months. (C) 2017 by the American College of Cardiology Foundation.