IMPORTANCE: Family caregivers of persons with advanced heart failure perform numerous daily tasks to assist their relatives and are at high risk for distress and poor quality of life. OBJECTIVE: To determine the effect of a nurse-led palliative care telehealth intervention (Educate, Nurture, Advise, Before Life Ends Comprehensive Heart Failure for Patients and Caregivers [ENABLE CHF-PC]) on quality of life and mood of family caregivers of persons with New York Heart Association Class III/IV heart failure over 16 weeks. DESIGN, SETTING, AND PARTICIPANTS: This single-blind randomized clinical trial enrolled caregivers aged 18 years and older who self-identified as an unpaid close friend or family member who knew the patient well and who was involved with their day-to-day medical care. Participants were recruited from outpatient heart failure clinics at a large academic tertiary care medical center and a Veterans Affairs medical center from August 2016 to October 2018. INTERVENTION: Four weekly psychosocial and problem-solving support telephonic sessions lasting between 20 and 60 minutes facilitated by a trained nurse coach plus monthly follow-up for 48 weeks. The usual care group received no additional intervention. MAIN OUTCOMES AND MEASURES: The primary outcomes were quality of life (measured using the Bakas Caregiver Outcomes Scale), mood (anxiety and/or depressive symptoms measured using the Hospital Anxiety and Depression Scale), and burden (measured using the Montgomery-Borgatta Caregiver Burden scales) over 16 weeks. Secondary outcomes were global health (measured using the PROMIS Global Health instrument) and positive aspects of caregiving. RESULTS: A total of 158 family caregivers were randomized, 82 to the intervention and 76 to usual care. The mean (SD) age was 57.9 (11.6) years, 135 (85.4%) were female, 82 (51.9%) were African American, and 103 (65.2%) were the patient's spouse or partner. At week 16, the mean (SE) Bakas Caregiver Outcomes Scale score was 66.9 (2.1) in the intervention group and 63.9 (1.7) in the usual care group; over 16 weeks, the mean (SE) Bakas Caregiver Outcomes Scale score improved 0.7 (1.7) points in the intervention group and 1.1 (1.6) points in the usual care group (difference, -0.4; 95% CI, -5.1 to 4.3; Cohen d = -0.03). At week 16, no relevant between-group differences were observed between the intervention and usual care groups for the Hospital Anxiety and Depression Scale anxiety measure (mean [SE] improvement from baseline, 0.3 [0.3] vs 0.4 [0.3]; difference, -0.1 [0.5]; d = -0.02) or depression measure (mean [SE] improvement from baseline, -0.2 [0.4] vs -0.3 [0.3]; difference, 0.1 [0.5]; d = 0.03). No between-group differences were observed in the Montgomery-Borgatta Caregiver Burden scales (d range, -0.18 to 0.0). Differences in secondary outcomes were also not significant (d range, -0.22 to 0.0). CONCLUSIONS AND RELEVANCE: This 2-site randomized clinical trial of a telehealth intervention for family caregivers of patients with advanced heart failure, more than half of whom were African American and most of whom were not distressed at baseline, did not demonstrate clinically better quality of life, mood, or burden compared with usual care over 16 weeks. Future interventions should target distressed caregivers and assess caregiver effects on patient outcomes. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02505425.