All patients from the practise of interest will be considered for the study and will be evaluated for inclusion and exclusion criteria as well as desire to participate. Criteria for participation is based on the design of above mentioned studies which showed benefits of PSM. 20 patients will then be randomized to two groups using a computer randomizer. Group A will be assigned to PSM for a duration of four months and then switched to physician-management for the remaining four months of the study. Group B will follow the opposing schedule. Patients in the PSM group will obtain their INR values from a community laboratory and then adjust their Warfarin dose. Dosage adjustments will be guided by dose adjustment nomograms (provided to patients) which are based on the recommendations of the BC Guidelines and Protocols Advisory Committee. Data from PSM will be compared to results from physician-management and also to accepted values for community anticoagulation control in the literature.