Background To evaluate the role of CT in detecting, characterizing, and guiding the management of pericardial effusion after CABG. Methods This cross-sectional study was conducted at Bacha Khan Medical College Mardan and its affiliated hospital between January 2023 and January 2024. Seventy-one adult patients who underwent CABG and subsequent postoperative CT chest imaging were included. Demographic, operative, and clinical data were collected. CT scans were assessed for effusion presence, size, distribution, attenuation, and associated thoracic findings. Effusion characteristics were correlated with perioperative variables and management outcomes. Statistical analysis was performed using SPSS v26, with p < 0.05 considered significant. Results Pericardial effusion was detected in 41 patients (57.7%), most commonly small (39.0%) or moderate (41.5%) in size; 19.5% were large. Circumferential distribution was seen in 65.9%, while 34.1% were loculated. Higher effusion size was significantly associated with longer cardiopulmonary bypass time (p = 0.03), therapeutic anticoagulation (p = 0.02), and CT signs of tamponade (p = 0.01). Moderate/large effusions had higher intervention rates (41.7% vs 4.5%, p < 0.001) and longer ICU stays (p < 0.001). CT also identified mediastinal hematomas (16.9%), pleural effusions (63.4%), and pneumopericardium (7.0%). Conclusion CT is a valuable complementary tool for detecting and characterizing postoperative pericardial effusions, especially when echocardiographic assessment is limited. Larger effusions on CT correlate with increased procedural intervention and adverse short-term outcomes, supporting its selective use in post-CABG surveillance.