Aim: Spirituality is a crucial dimension in human health. However, it is often overlooked in patients with heart failure (HF) in Iran. Thus, the purpose of this study was to determine the relationship between spiritual wellbeing, life expectancy and quality-of-life (QOL) in patients with HF. Methods: This cross-sectional study was performed with 150 HF patients, who were enrolled through convenience sampling. Data were collected using a questionnaire comprising four parts: the Minnesota Living with Heart Failure Questionnaire, Schneider’s life expectancy instrument, Ellison’s and Paulotzin’s (1982) Spiritual Well-Being Scale, and a demographic checklist. SPSS software was used for data analysis. Results: In this study, mean and standard deviation of QOL, life expectancy and spiritual wellbeing were 41.82±19.17, 30.20±4.58 and 87.80±5.28 respectively. There was a significant relationship between spiritual wellbeing and quality of life (r=-0.633, P<0.001) and also life expectancy (r=0.544, P<0.001). Quality of life and life expectancy were significantly higher in men than in women. Linear regression tests showed that the existential and religious dimensions of spirituality could influence 44.9% of the QOL variance (F=54.54, P<0.001) and increased values of existential spirituality would improve QOL by an average of 3.45 units. Improving life expectancy also raised QOL by 14.0% (F=21.26, P<0.001). This study also demonstrated that life expectancy is impacted by spiritual health, with a variance of 34.2%, in which the role of existential-spiritual health is of particular significance (t=7.10, P<0.001). Conclusion: The results revealed that spiritual wellbeing, especially the existential type, enhances life expectancy and quality-of-life among HF patients. Therefore, it is recommended that healthcare professionals design a comprehensive and supportive care model for the promotion of spiritual wellbeing in HF patients.