Background Late tamponade after cardiac surgery is a clinically obscure condition presenting significant diagnostic challenges, since it may be difficult to detect using routine imaging studies. This study is aimed to investigate the diagnostic value of transthoracic echocardiography (TTE) and contrast-enhanced computerized tomography (cCT) in the diagnosis of late tamponade following open-heart surgery. Methods A total of 88 patients who underwent reoperation after cardiac surgery with suspected late cardiac tamponade were included in this retrospective study. All the patients had TTE and cCT examinations before reoperation. The diagnostic values of these imaging modalities were investigated using surgically confirmed late tamponade as the standard. Results The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of an optimal cutoff value of greater than 3.1 cm pericardial fluid thickness on cCT images for predicting surgically confirmed late tamponade were 91.4%, 66.6%, 97.4%, 36.3%, and 89.7%, respectively. Accordingly, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of TTE for the diagnosis of late tamponade were 34.1%, 50.0%, 90.3%, 5.2%, and 35.2%, respectively. The cCT provided false-negative results in seven patients (8%), while this figure was 54 (61.4%) for that of TTE. Conclusion Computerized tomography imaging seems to represent a superior imaging technique in terms of visualizing the intrapericardial fluid collections after cardiac surgery and has the potential to readily diagnose late tamponade and effectively prevent unnecessary morbidity and mortality.