Background/Objectives: New-onset atrial fibrillation (AF) after cardiac surgery is associated with patient-important outcomes. Uncertainty persists regarding its prevention, detection, and management. This review seeks to identify, compile, and describe ongoing registered research studies involving patients with or at risk for post-operative AF (POAF) after cardiac surgery. Methods: We searched clinical trial registries in January 2023 for studies focusing on POAF prediction, prevention, detection, or management. We extracted data from each record and performed descriptive analyses. Results: In total, 121 studies met the eligibility criteria, including 82 randomized trials. Prevention studies are the most common (n = 77, 63.6%), followed by prediction (n = 21, 17.4%), management (n = 16, 13.2%), and detection studies (n = 7, 5.8%). POAF after cardiac surgery is an area of active research. Conclusions: There are many ongoing randomized prevention studies. However, two major clinical gaps persist; future randomized trials should compare rate and rhythm control in patients who develop POAF, and long-term follow-up studies should investigate strategies to monitor for AF recurrence in patients with POAF.