BACKGROUND: After transcatheter aortic valve implantation, early leaflet thickening, presumably reflecting thrombus, has recently been described on computed tomography angiography (CTA) in ~10% of the patients. We sought to investigate the impact of the antithrombotic regimen on the course of leaflet thickening. METHODS: The study comprised 51 patients with leaflet thickening. Based on the time period, patients without an established indication for anticoagulation were put on phenprocoumon plus clopidogrel for at least 3 months or on dual antiplatelet therapy with aspirin and clopidogrel. Follow-up CTAs were evaluated for leaflet restriction, assessed by four-point-grading score, and maximal thickness. FINDINGS: The anticoagulation and the dual antiplatelet therapy group comprised 29 and 22 patients, respectively. After a median of 86 days, we obtained follow-up CTAs in 22 patients on anticoagulation and in 16 patients on dual antiplatelet therapy. Leaflet thickening progressed in 11 on dual antiplatelet therapy, but always regressed onanticoagulation. The course of leaflet restriction and maximal thickness was significantly different between the two groups (P < 0.001): in the dual antiplatelet therapy group, maximal thickness increased by a mean of 1.37 ± 1.67 mm (P = 0.005) and leaflet restriction score by a median 1[quartiles 0;2] (P = 0.013), whereas in the anticoagulation group, maximal thickness regressed by 2.57 ± 1.52 mm (P < 0.001) and leaflet restriction score decreased by 1[-4;0] (P = 0.001). After a median of 91 days after discontinuation of anticoagulation, CTA performed in ten patients revealed a significant recurrent increase in leaflet restriction score and maximal thickness (P = 0.023, P = 0.007). In the entire cohort, changes in leaflet restriction correlated significantly with changes in transvalvular pressure gradients (r = 0.511, P < 0.001). INTERPRETATION: The course of leaflet restriction was fundamentally different depending on the presence or absence of anticoagulation, with consistent regression under phenprocoumon, but mostly progression under antiplatelet therapy alone. Changes in leaflet restriction were associated with changes in transvalvular pressure gradients.