Data show that anticoagulation with a VKA is protective against valve thrombosis (OR: 0.11; 95% CI: 0.07 0.2) and thromboembolic events (OR: 0.21; 95% CI: 0.16 0.27). It is preferable to specify a single INR target for each patient and to recognize that the acceptable range includes 0.5 INR units on each side of this target. A spe- cific target is preferable because it reduces the likelihood of patients having INR values consis- tently near the upper or lower boundary of the range. Fluctuations in INR are associated with an increased incidence of complications in patients with prosthetic heart valves.19,38 2. The rate of thromboembolism in patients with a bileaflet mechanical AVR treated with a VKA is estimated to be 0.53% per patient-year over the INR range of 2.0 to 4.5. In a large retrospective study, adverse events increased if the INR was >4.0 in patients with a mechanical AVR. 