Patients with a history of SAVR or TAVR with bioprosthetic aortic valves undergo cardiac contrast CT imaging and transthoracic echocardiography to evaluate structural and functional integrity of the aortic valves. The imaging studies will be performed at least 48-hours after TAVR/SAVR. Patients with prosthetic valve abnormalities suggestive of thrombus will be administered anticoagulation therapy with Vitamin K antagonists (Warfarin) for 3 months with goal International Normalized Ratio (INR) 2-3, followed by repeat contrast CT of the chest and transthoracic imaging. Repeat imaging following 3 months of anticoagulation therapy is performed to evaluate the response to anticoagulation therapy. INR levels will be monitored and warfarin dose adjusted to maintain target INR 2-3.