The goal of this clinical trial is to learn if an epicardial radiofrequency left atrial posterior wall isolation (box lesion ablation) prevents atrial fibrillation after cardiac surgery. The main question it aims to answer is: \- Does box lesion ablation lower the number of patients experiencing de-novo atrial fibrillation requiring any treatment after cardiac surgery? Researchers will compare box lesion ablation to no ablation to see if ablation prevents postoperative atrial fibrillation. Participants will undergo ablation or no ablation at the time of other cardiac surgery. Data will be collected while in hospital. Additional information will be collected on 30th day after surgery by telephone call or during a visit.