Aims Self-care, an essential component of heart failure (HF) treatment, is inadequate in most patients. We evaluated if motivational interviewing (MI) (i) improves patient self-care maintenance (primary endpoint; e.g. taking medications), self-care management (e.g. responding to symptoms) and self-care confidence (or self-efficacy) 3 months after enrolment; (ii) changes self-care over 1 year, and (iii) augments patient self-care if informal caregivers are involved. Methods and results Parallel randomized controlled trial (1:1:1). A sample of 510 patients (median 74 years, 58% male) and caregivers (median 55 years, 75% female) was randomized to Arm 1 (MI only for patients), Arm 2 (MI for patients and caregivers), or Arm 3 (usual care). The intervention in Arms 1 and 2 consisted of one face-to-face MI session with three telephone contacts. Self-care was evaluated with the Self-Care of HF Index measuring self-care maintenance, management, and confidence. Scores on each scale range from 0 to 100 with higher scores indicating better self-care; ≥70 is considered adequate. At 3 months, self-care maintenance improved 6.99, 7.42 and 2.58 points in Arms 1, 2, and 3, respectively (P = 0.028). Self-care maintenance was adequate in 18.4%, 19.4%, and 9.2% of patients in Arms 1, 2 and 3, respectively (P = 0.016). Over 1 year, self-care maintenance, management, and confidence scores in Arms 1 and 2 were significantly higher than in Arm 3 in several follow-ups. Over 1 year, Arm 2 had the best scores in self-care management.Conclusions MI significantly improved self-care in HF patients. Including caregivers may potentiate the effect, especially in self-care management. ClinicalTrial.gov, identifier: NCT02894502.