Background Heart failure (HF) self-care is poor in developed countries like the United States, but little is known about self-care in developing countries. Methods and Results A total of 2082 adults from 2 developed (United States and Australia) and 2 developing countries (Thailand and Mexico) were studied in a descriptive, comparative study. Self-care was measured using the Self-Care of HF Index, which provided scores on self-care maintenance, management, and confidence. Data were analyzed using regression analysis after demographic (age, gender, education), clinical (functional status, experience with the diagnosis, comorbid conditions), and setting of enrollment (hospital or clinic) differences were controlled. When adequate self-care was defined as a standardized score ≥70%, self-care was inadequate in most scales in most groups. Self-care maintenance was highest in the Australian sample and lowest in the Thai sample (P < .001). Self-care management was highest in the US sample and lowest in the Thai sample (P < .001). Self-care confidence was highest in the Mexican sample and lowest in the Thai sample (P < .001). Determinants differed for the three types of self-care (eg, experience with HF was associated only with self-care maintenance). Conclusion Interventions aimed at improving self-care are greatly needed in both the developed and the developing countries studied.