Cardiovascular disease (CVD) is a major public health problem and a primary cause of morbidity and mortality in the United States. Regular physical activity is recommended for prevention and management of CVD. Despite the cardiovascular health benefits of physical activity most adults are physically inactive. Therefore, the aim of this dissertation was to examine the factors associated with adherence to physical activity among individuals with or without CVD. The first paper is a report of a study conducted to examine which baseline demographic (age, gender, marital status, socioeconomic status, and place of residency), psychosocial (social support, depression, anxiety, and fatalism), and clinical (past history of exercising, comorbidity, and health literacy) variables predicted successful adoption of the active lifestyle recommendation of increasing moderate-to-vigorous physical activity by an accumulated 15 minutes or more each day following a CVD risk reduction intervention and 2) to identify which of those same factors predicted dropout from the CVD risk reduction intervention among at-risk individuals in rural America. The study sample consisted of 399 rural Americans. The results revealed that a higher anxiety level was a predictor of active lifestyle modification following a CVD risk reduction intervention. In contrast, younger age and low health literacy were predictors of dropout from a CVD risk reduction intervention. The second paper is a literature review of studies investigating the factors that affected enrollment in cardiac rehabilitation in patients with heart failure (HF). The aims of this review were to: (a) describe enrollment rates of patients with HF in cardiac rehabilitation programs, (b) review the literature on factors affecting enrollment of patients with HF, and (c) identify areas for future research. It is difficult to draw conclusion about enrollment rates because the period of time after hospital discharge that enrollment was measured varied across studies. A wide array of demographic, psychosocial, and clinical variables have been identified as potential barriers of enrollment in cardiac rehabilitation programs. Additional research including patients with HF is needed. The third paper is a report of a cross-sectional study of 279 patients with HF. The aims were to determine 1) the amount of variance in the functional status predicted by depressive symptoms, perceived control, self-rated health, HF self-care maintenance behaviors, and serum N-terminal pro-B-type natriuretic peptide ( NT-pro-BNP) biomarker of cardiac dysfunction in patients with HF and 2) whether NT-pro-BNP mediated the relationship between self-care maintenance behaviors and functional status. Depressive symptoms, poor self-rated health, non-adherence to physical activity, and greater serum NT-pro-BNP levels were independently associated with worse perceptions of functional status. Serum NT-pro-BNP levels partially mediated the association between adherence to physical activity and perception of functional status. The findings from this dissertation provided further evidence of the importance of adherence to physical activity and identify key variables that promote participation in interventions to promote heart healthy lifestyles and adherence to physical activity.