Background: The Freestyle aortic root bio prosthesis is a complete porcine aortic root implanted by different techniques: sub coronary, root inclusion, or complete aortic root replacement. The choice among the three implant techniques depends on surgeon preference or upon the pathology encountered. Its implantation is done by open heart surgery. The study aimed to trace the prevalence of sub clinical leaflet thrombosis in patient underwent free style aortic valve replacement, and how far is the need for anticoagulation therapy to protect the patients from being involved in transient ischemic attacks (TIAs) or strokes. Method: This study enrolled 47 patients underwent Freestyle aortic valve and had MDCT at least with two follow up point interval post operative. We evaluated the cusp structure and possible sub clinical thrombosis using a retrospective ECG gated CT angiographic study. Results: We observed 22 cases with positive thrombus out of 47 with percentage of 46%, with negative relationship between thrombus formation and oral anticoagulant taking. The cumulative incidence of thrombus was increasing over years. Conclusion: Sub clinical thrombus formation is a common complication over Freestyle bioprosthetic valve and makes oral anti-coagulant taking mandatory