Does Low Dose Oral Vitamin K Improve International Normalized Ratio (INR) Stability?

Inclusion Criteria: * Warfarin therapy administered to a target INR of 2.0 to 3.0 Exclusion Criteria: * Out of range INR on day of screening - enrolment will only occur if the patient's INR on the day of screening is between 1.8 and 3.4 (inclusive) - if the INR is outside this range the patient will be re-screened when the INR is within this range. * Recent warfarin initiation - all patients must have received warfarin for a minimum of 3 months * Planned termination or extended temporary interruption of warfarin within 6 months or anticipated survival of less than 6 months * Known severe liver disease, known excess alcohol consumption , known malabsorption syndrome or inability to take oral medications * Use of medications known to interfere with warfarin and whose dose is likely to change over the course of the study (e.g. barbiturates, rifampin etc.) * Known allergy to vitamin K * Inability or unwillingness to follow study procedures or provide consent * Prior participation in this study, or participating in a competing study which may impact INR control