BACKGROUND: The role of stress in the prognosis of heart failure (HF) is unclear. This study investigated whether the death of a close family member, a severe source of stress, is associated with mortality in HF. OBJECTIVES: This study assessed whether the death of a close family member is associated with mortality in HF. METHODS: Patients from the Swedish Heart Failure Registry during 2000-2018 and/or in the Swedish Patient Register with a primary diagnosis of HF during 1987-2018 (N = 490,527) were included in this study. Information was obtained on death of family members (children, partner, grandchildren, siblings, and parents), mortality, sociodemographic variables, and health-related factors from several population-based registers. The association between bereavement and mortality was analyzed by using Poisson regression. RESULTS: Loss of a family member was associated with an increased risk of dying (adjusted relative risk: 1.29; 95% CI: 1.27-1.30). The association was present not only in case of the family member's cardiovascular deaths and other natural deaths but also in case of unnatural deaths. The risk was higher for 2 losses than for 1 loss and highest in the first week after the loss. The association between bereavement and an increased mortality risk was observed for the death of a child, spouse/partner, grandchild, and sibling but not of a parent. CONCLUSIONS: Death of a family member was associated with an increased risk of mortality among patients with HF. Further studies are needed to investigate whether less severe sources of stress can also contribute to poor prognosis in HF and to explore the mechanisms underlying this association.