Valve replacement is the only definitive treatment for patients with severe valvular heart disease. Mechanical valves are usually preferred over biological valves in younger patients because they are more durable but require lifelong anticoagulation with a vitamin K antagonist (VKA) to prevent thromboembolism. Bioprosthetic valves are associated with low rates of clinical thromboembolism, thereby obviating the need for long-term anticoagulation. However, newer imaging technologies (4D echocardiography, 4D computed tomography) have demonstrated subclinical valve thrombosis in 10–20% of patients within the first year of implantation, which may be a cause of structural valve deterioration. Accordingly, there is increasing interest in the optimal choice of antithrombotic therapy in these patients, particularly during the first 3 months after valve implantation when the risk of subclinical thromboembolism appears to be greatest.