Patient Exclusion Criteria

• Unable to complete the study materials (questionnaires) with or without assistance (for example, those with dementia);
• Being started on anticoagulation intended to last < 30 days or whose target INR is < 2.0;
• History of treatment with warfarin and a known dose requirement (as they should be restarted on the previous dose);
• Genotype (CYP2C9 or VKORC1) known to participant from prior testing or available in subject’s medical record;
• The treating physician does not agree to use the recommended warfarin dose or feels that the patient should not be enrolled in the study;