The outcome of warfarin therapy varies among individuals due to factors such as genetics, age, ethnicity, diet and weight which have been shown to have varying impact on therapeutic anticoagulation [3-10]. Although many studies have reported benefits of the use of these parameters to determine warfarin doses, clinically guided management still relies heavily on monitoring International Normalized Ratio (INR). The primary objective of the study was to examine the prevalence of therapeutic anticoagulation with warfarin among patients registered in a setting where clinically guided management is the only available system for monitoring warfarin efficacy. The secondary objectives of the study include an assessment of the differences between subjects that are within the target INR range (therapeutic anticoagulation) and those subjects outside the target INR (non-therapeutic anticoagulation). Methods This was a cross-sectional, observational, convenience sample study of adults (at least 18 years of age) on warfarin maintenance therapy recruited from the University Hospital of the West Indies Cardiology Clinic in the two time periods (January 2014-May 2014 and February 2015-October 2015). Inclusion criteria also required subjects to be warfarin for more than one month and self-report of good compliance. Informed consent guidelines were followed and all subjects recruited in this study consented to participate. After Informed Consent was obtained, information recorded included daily dose, date of initiation, and indication for warfarin therapy. Also recorded for each subjects was age, weight, height, gender, ethnicity and concomitantly administered drugs. INR assessment A single sample of one drop (≥ 8µL) of capillary blood from each patient, obtained by pinprick was used to obtain INR