Summary Background Incomplete revascularisation is common after percutaneous coronary intervention and is associated with increased mortality and adverse cardiovascular events. We aimed to assess whether adjunctive anti-ischaemic pharmacotherapy with ranolazine would improve the prognosis of patients with incomplete revascularisation after percutaneous coronary intervention. Methods We performed this multicentre, randomised, parallel-group, double-blind, placebo-controlled, event-driven trial at 245 centres in 15 countries in Europe, Israel, Russia, and the USA. Patients (aged ≥18 years) with a history of chronic angina with incomplete revascularisation after percutaneous coronary intervention (defined as one or more lesions with ≥50% diameter stenosis in a coronary artery ≥2 mm diameter) were randomly assigned (1:1), via an interactive web-based block randomisation system (block sizes of ten), to receive either twice-daily oral ranolazine 1000 mg or matching placebo. Randomisation was stratified by diabetes history (presence vs absence) and acute coronary syndrome presentation (acute coronary syndrome vs non-acute coronary syndrome). Study investigators, including all research teams, and patients were masked to treatment allocation. The primary endpoint was time to first occurrence of ischaemia-driven revascularisation or ischaemia-driven hospitalisation without revascularisation. Analysis was by intention to treat. This study is registered at ClinicalTrials.gov , number NCT01442038. Findings Between Nov 3, 2011, and May 27, 2013, we randomly assigned 2651 patients to receive ranolazine (n=1332) or placebo (n=1319); 2604 (98%) patients comprised the full analysis set. After a median follow-up of 643 days (IQR 575–758), the composite primary endpoint occurred in 345 (26%) patients assigned to ranolazine and 364 (28%) patients assigned to placebo (hazard ratio 0·95, 95% CI 0·82–1·10; p=0·48). Incidence of ischaemia-driven revascularisation and ischaemia-driven hospitalisation did not differ significantly between groups. 189 (14%) patients in the ranolazine group and 137 (11%) patients in the placebo group discontinued study drug because of an adverse event (p=0·04). Interpretation Ranolazine did not reduce the composite rate of ischaemia-driven revascularisation or hospitalisation without revascularisation in patients with a history of chronic angina who had incomplete revascularisation after percutaneous coronary intervention. Further studies are warranted to establish whether other treatment could be effective in improving the prognosis of high-risk patients in this population. Funding Gilead Sciences, Menarini.