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The On-X valve is a newer generation mechanical bileaflet valve. Its key features include the use of pure pyrolytic carbon (devoid of silicon), a length-to-diameter ratio similar to a native valve, an inlet flared orifice, a leaflet opening up to 90 degrees, a shorter leaflet closing angle, a 2-point leaflet contact, and an actuated pivot. These features have translated into increased strength, improved valve hemodynamics, reduced hemolysis, and thrombogenicity. The 2014 American Heart Association/American College of Cardiology guidelines for the management of patients with valvular heart disease recommend an international normalized ratio (INR) of 2.5 (range, 2–3) in patients with a mechanical valve at the aortic position. However, based on the results of the Prospective Randomized On-X Anticoagulation Clinical Trial (PROACT), the Food and Drug Administration approved this valve in April 2015 in the aortic …