Aortic valve replacement (AVR) is the second most common cardiothoracic procedure performed in the United States (1) and Europe (2). Surgically or percutaneously implanted, the results of AVRs are uniformly good and the number of patients have been steadily increasing over the last decades (3). Although most of the newly implanted devices are tissue valves, yet a sizable number are mechanical especially in young patients with rheumatic disease. The latter group is predominant in non-Caucasian populations where the rheumatic disease is the most common aetiology (4).In parallel, during the same years computed tomography (CT) scan technology evolved substantially offering excellent resolution and the ability to identify the commonest and most challenging complications of AVR (5). In particular, ECG-gated CT scan proved to be more reliable than echocardiography in identifying pannus, the most insidious long-term complication of mechanical valves. CT scan techniqueImages are usually acquired using retrospective ECGgated protocols with cardiac phase reconstruction at 5% to 10% RR interval increments. Both systolic (at 20% to 40% of RR interval) and diastolic phase (at 70% to 90% RR interval) are usually necessary. With these modalities, more than 90% of the valves can be accurately evaluated (6). As opposed to retrospective triggering, prospective ECG-gated protocols tend to generate less artifacts and require lesser radiation doses. However, they can be used only in patients with regular heart rate. When the patients are in atrial fibrillation, short acting beta-blockers can be used during the acquisition phase. However, with faster heart rates best results are obtained with dual source CT scan.CT data are reconstructed by a separate workstation for post-processing where oblique coronal or oblique sagittal images of the aortic root are assembled (Figure 1). By using a multiplanar image technique, profile and enface views of the prosthetic aortic valve showing the least amount of motion artifacts are generated. The presence or absence of a subprosthetic pannus is determined by the examiner as the appearance of a low-attenuation lesion or a calcified lesion Abstract: Obstruction of a mechanical aortic valve by pannus formation at the subvalvular level is a major long-term complication of aortic valve replacement (AVR). In fact, pannus is sometime difficult to differentiate from patient-prosthesis mismatch or valve thrombosis. In most cases cine-angiography and echocardiography, either transthoracic or transesophageal, cannot correctly visualize the complication when the leaflets show a normal mobility. Recent technological refinements made this difficult diagnosis possible by ECG-gated computed tomography (CT) scan which shows adequate images in 90% of the cases and can differentiate pannus from fresh and organized thrombus.