Background: 20-40% of patients with ischemic heart disease managed with coronary artery bypass grafting (CABG) surgeries face the risk of postoperative atrial fibrillation (POAF), which is a known hazardous outcome. Being a well-known arrhythmogenic pathway, surgical excision of the ligament of Marshall may, theoretically, lower the incidence of POAF. Aim: In this study, we aimed to assess the safety and efficacy of prophylactic LoM resection in preventing POAF after on-pump CABG (ON-CAB.). Methods: 220 patients at elevated risk for POAF undergoing elective ON-CAB were randomized to receive either standard CABG alone (n = 110) or adjunctive LoM resection (n = 110) in this multicenter, randomized, assessor- and patient-blinded study with unblinded surgeons. ECG-verified POAF occurring within seven days was the primary outcome. Mortality, use of resources, and pharmaceutical therapy were secondary outcomes.