Cardiac rehabilitation patients improve cardiorespiratory fitness and quality of life, yet therapeutic processes that produce these changes remain unknown. A cross-lagged panel design was used to determine whether early-treatment enhancement of self-efficacy regarding abilities to change diet and exercise habits and the quality of the patient-staff working alliance predicted late-treatment changes in a wide range of outcomes, but not vice versa. Eighty cardiac patients participating in a 12-week program completed measures at early, mid- and late treatment. Early-treatment changes in exercise self-efficacy predicted late-treatment changes in activity level, depression, and working alliance, but not vice versa. Diet self-efficacy changes correlated with concurrent changes in fat intake and body weight. Early-treatment changes in cardiorespiratory fitness and activity level predicted late-treatment changes in working alliance, but not vice versa. Findings suggest that increased exercise self-efficacy represents an important therapeutic mechanism by which rehabilitation gains are realized