Background: Medication non-adherence contributes significantly to sub-optimum care, for reasons that could be unique to specific localities. The study sought to identify reasons for non-adherence and associated factors in cardiac clinic attendees at a leading tertiary health institution in Trinidad and Tobago.Methods: This cross-sectional study included a convenience sample of cardiac clinic attendees. The data collection instrument was a questionnaire comprising items regarding socio-demographic characteristics, medical history, social support and reasons for medication non-adherence. Data were collected between March and July, 2016. Non-adherence was identified with total scores of >1 using selected similar questions to that used in the Morisky four-item adherence instrument. Data analyses involved both descriptive and inferential methods.Results: Non-adherent patients represented the largest proportion of participants (n=270, 78.3%). Participants were predominantly women, aged >50 years, of Indo-Trinidadian descent, married, and unemployed. Carelessness (n=251, 93.0%), ceasing medication use when feeling well (n=217, 80.4%), forgetfulness (n=187, 69.3%), and ceasing medication use when feeling worse (n=151, 50.6%) were the leading reasons for non-adherence, followed by unpleasant effects of medication and cost (n=144, 53.3%). Associated factors included feeling that one would become more ill upon ceasing medication use (p=0.003), the importance of understanding the reasons for taking medication (p=0.017), the importance of following physicians’ instructions (p=0.023), and educational level (p=0.040).Conclusions: Effective communication regarding patients’ concerns and potential adverse medication effects between patients and healthcare providers could promote greater adherence.