Despite the documented evidence of the benefits of cardiac rehabilitation (CR) in enhancing recovery and reducing mortality following a myocardial infarction, only about one third of patients participate in such programs. Adherence to these programs is an even bigger problem, with only about one third maintaining attendance in these programs after 6 months. This review summarizes research that has investigated barriers to participation and adherence to CR programs. Some consistent factors found to be associated with participation in CR programs include lack of referral by physicians, associated illness, specific cardiac diagnoses, reimbursement, self-efficacy, perceived benefits of CR, distance and transportation, self-concept, self-motivation, family composition, social support, self-esteem, and occupation. Factors associated with non-adherence include being older, female gender, having fewer years of formal education, perceiving the benefits of CR, having angina, and being less physically active during leisure time. However, many of the studies have methodologic flaws, with very few controlled, randomized studies, making the findings tentative. Problems in objectively measuring adherence to unstructured, non-hospital-based programs, which are an increasingly popular alternative to traditional programs, are discussed. Suggestions for reducing barriers to participation and adherence to CR programs, as well as for future research aimed at clearly identifying these barriers, are discussed.