The primary hypothesis of this trial is that changes in oral vitamin K intake, based on simple food registries, may be superior to conventional changes in doses of medications in order to stabilize chronic oral anticoagulation.

Inclusion Criteria:

• Patients with any clinical indication for chronic oral anticoagulation with one INR level out of target, without a clear clinical cause for INR instability (unplanned changes in coumadin medications, other pharmacological interactions, clinical illnesses and laboratory errors).

Exclusion Criteria:

• Clinical evidence of bleeding or thrombosis.
• INR > 4 or INR < 1,5.