When a patient has an aortic valve that requires replacement because the native valve is diseased, 2 types of valves can be used—mechanical valves or bioprosthetic valves, also known as tissue valves. Bioprosthetic valves are less durable than mechanical values but generally do not require the long-term use of anticoagulation; they are often recommended in older patients. Mechanical valves require therapeutic anticoagulation because of the risk for valve thrombosis, a catastrophic and life-threatening complication. The use of bioprosthetic valves increased from 38% in the period from 1998 to 2001 to 64% in the period from 2007 to 2011.1