Caregivers of individuals with heart failure are at high risk for diminished quality of life because of the energy involved in providing necessary care. Caring for someone with chronic heart failure can affect caregivers' physical, psychological, and social health, collectively referred to as the burden of care, and may also affect family functioning. The current cross-sectional study aimed to investigate the relationship between caregiver burden and family functioning in caregivers of older adults with heart failure in southeastern Iran using the Zarit Burden Inventory and the Family Assessment Device based on the McMaster Model of Family Functioning. The Pearson correlation coefficient, independent t test, and analysis of variance were used to determine relationships among variables. Results showed a significant correlation between burden of care and total score of family functioning. Therefore, it is necessary to take measures to reduce burden of care for caregivers through education and support programs and to improve their family functioning and quality of life.