Diltiazem has been used during the perioperative period in patients undergoing coronary artery bypass grafting (CABG) to prevent arterial graft spasm. However, its long-term outcome effects remain unclear. Patient records obtained from the Society of Thoracic Surgeons and the Geisinger Clinic electronic health records between October 2008 and October 2018 were screened. Adult patients who had isolated CABG with cardiopulmonary bypass were included. Cohorts of patients who received diltiazem (DILT) and those who did not (non-DILT) were matched by propensity scores based on age, gender, surgical year, Society of Thoracic Surgeons mortality and morbidity scores, and number of arterial grafts. Incidence rate ratios (IRRs) were estimated for DILT vs non-DILT on short-term adverse outcomes. Long-term survival over time was compared between DILT vs non-DILT using Kaplan–Meier curves. Among the 1004 patients included in the analyses, IRRs for the DILT group relative to the non-DILT group were: 30-day all-cause mortality, IRR: 2.33, 95% confidence interval (CI): 0.91–5.96, P=0.07; postoperative myocardial ischaemia, IRR: 1.10, 95% CI: 0.60–2.02, P=0.75; new onset atrial fibrillation, IRR: 1.06, 95% CI: 0.78–1.43, P=0.73; stroke/transient ischaemic attack, IRR: 0.76, 95% CI: 0.17–3.38, P=0.71. For long-term survival, Kaplan–Meier curves stratified by diltiazem revealed no differences in survival rates between DILT and non-DILT groups. For patients undergoing on-pump CABG, perioperative diltiazem therapy did not show significant short- or long-term outcome advantages over those who did not receive diltiazem.