What is the problem to be addressed ? Although warfarin is a highly effective anticoagulant, it causes bleeding. The risk of bleeding in an individual is increased by a number of factors, including age, gender and previous hemorrhage. However, the single strongest predictor of hemorrhage is excessive prolongation of the international normalized ratio (INR). We have shown that low-dose oral vitamin K reliably reduces an excessively prolonged INR; we hypothesize this treatment will also reduce the risk of hemorrhage without increasing the risk of thrombosis. The objective of this study is to demonstrate that low dose oral vitamin K improves the safety of oral anticoagulant therapy, by reducing the risk of bleeding without causing thrombosis, in patients presenting with INR values of more than 4.5.