Self-care is challenging but we previously demonstrated that motivational interviewing (MI) was effective in improving heart failure (HF) self-care. OBJECTIVE: To identify the mechanisms of intervention effectiveness by elucidating the MI techniques used and the relationship between the techniques and changes in self-care. METHODS: Audiotaped sessions (first and subsequent sessions) from 8 participants were transcribed verbatim and coded to evaluate changes in self-care. Using a sequential mixed method design, quantitative and qualitative self-care data were triangulated; congruence was 97%. The MI techniques used and mechanisms of intervention effectiveness were identified from the qualitative data. RESULTS: Three MI techniques used were related to improved self-care: 1) reflection and reframing, 2) genuine empathy, affirmation, and humor, and 2) individualized problem solving. These techniques stimulated openness to goal setting, positive self-talk, perceived ability to overcome barriers, and change talk. The mechanisms by which the techniques achieved the desired outcomes were the development of discrepancy and self-efficacy, which are consistent with the principles of MI. CONCLUSION: This study contributes to clarifying the mechanism by which MI facilitates behavioral change. PRACTICE IMPLICATIONS: Using MI to discuss self-care can help to overcome barriers and engage HF patients in goal setting for behavior change.