Background: Heart failure - as a chronic disease - is a growing problem in communities in such a way that not only individuals but also family members and friends are being affected. The main role of self-care after heart failure has been demonstrated by research. Self-efficacy and social support are associated with self-care. The aim of this study is to explore the role of self-efficacy as a mediator in the relationship between social support and self-care in patients with heart failure. Methods: This descriptive and correlational study was conducted on heart failure patients in 2016. As many as 149 patients were examined, based on inclusion and exclusion criteria, and were selected for sampling. For data collection, a demographic information questionnaire, self-care behaviour scale, general selfefficacy (GSE), and social support scale were used. In addition, the Pearson correlation coefficient and Sobel test were also conducted. Results: Sobel test results for understanding the mediating role in the relationship between perceived social support and self-care was –5.43, p<0.01. The correlation between social support and self-care was -0.518, p<0.01. Conclusion: This study showed that self-efficacy as a mediator helps explain the relationship between social support and self-care and there was negative correlation between social support and lack of self-care.