Both positive affect and optimism are associated with cardiovascular health and engagement in cardiac health behaviors. Health behavior interventions in patients with cardiovascular disease have incorporated positive psychology (PP) exercises to enhance these psychological constructs, with an aim of improving diet, medication adherence, or physical activity. However, there has been little research into whether improvements in these constructs are associated with improvements in health behavior adherence. We performed a secondary analysis of data from a factorial trial of a PP-based health behavior intervention in 128 patients following acute coronary syndrome to examine the relationships between changes in positive psychological constructs (positive affect [Positive and Negative Affect Schedule] and optimism [Life Orientation Test – Revised]) and adherence to physical activity, diet, and medications (Medical Outcomes Study – Specific Adherence Scale). The PP-based intervention led to significant pre-post improvements in both optimism and positive affect. In mixed effects regression analyses, change in positive affect was significantly associated with improved health behavior adherence (β=0.044, 95% CI=0.000-0.089, p=.049), while change in optimism was not (β=0.027, 95% CI=-0.052-0.106, p=.50). Though further research is needed, these findings suggest that positive affect may be a better treatment target for health behavior interventions that utilize PP principles.