Key Points Question Does an intervention aimed at improving guideline adherence for the management of acute heart failure, including intensive intravenous nitrate therapy and management of precipitating factors, improve hospital discharge and survival at 30 days? Findings In this stepped-wedge cluster randomized trial that included 503 patients 75 years and older who presented to the emergency department with acute heart failure, implementation of an early and comprehensive care bundle compared with usual care improved guideline adherence, but had no significant effect on number of days alive and out of hospital at 30 days (median of 19 d in both groups). Meanings This emergency department care bundle did not improve 30-day outcomes among older patients with acute heart failure. Abstract Importance Clinical guidelines for the early management of acute heart failure in the emergency department (ED) setting are based on only moderate levels of evidence, with subsequent low adherence to these guidelines. Objective To test the effect of an early guideline-recommended care bundle on short-term prognosis in older patients with acute heart failure in the ED. Design, Setting, and Participants Stepped-wedge cluster randomized trial in 15 EDs in France of 503 patients 75 years and older with a diagnosis of acute heart failure in the ED from December 2018 to September 2019 and followed up for 30 days until October 2019. Interventions A care bundle that included early intravenous nitrate boluses; management of precipitating factors, such as acute coronary syndrome, infection, or atrial fibrillation; and moderate dose of intravenous diuretics (n = 200). In the control group, patient care was left to the discretion of the treating emergency physician (n = 303). Each center was randomized to the order in which they switched to the “intervention period.” After the initial 4-week control period for all centers, 1 center entered in the intervention period every 2 weeks. Main Outcomes and Measures The primary end point was the number of days alive and out of hospital at 30 days. Secondary outcomes included 30-day all-cause mortality, 30-day cardiovascular mortality, unscheduled readmission, length of hospital stay, and kidney impairment. Results Among 503 patients who were randomized (median age, 87 years; 298 [59%] women), 502 were analyzed. In the intervention group, patients received a median (interquartile range) of 27.0 (9-54) mg of intravenous nitrates in the first 4 hours vs 4.0 (2.0-6.0) mg in the control group (adjusted difference, 23.8 [95% CI, 13.5-34.1]). There was a significantly higher percentage of patients in the intervention group treated for their precipitating factors than in the control group (58.8% vs 31.9%; adjusted difference, 31.1% [95% CI, 14.3%-47.9%]). There was no statistically significant difference in the primary end point of the number of days alive and out of hospital at 30 days (median [interquartile range], 19 [0- 24] d in both groups; adjusted difference, −1.9 [95% CI, −6.6 to 2.8]; adjusted ratio, 0.88 [95% CI, 0.64-1.21]). At 30 days, there was no significant difference between the intervention and control groups in mortality (8.0% vs 9.7%; adjusted difference, 4.1% [95% CI, −17.2% to 25.3%]), cardiovascular mortality (5.0% vs 7.4%; adjusted difference, 2.1% [95% CI, −15.5% to 19.8%]), unscheduled readmission (14.3% vs 15.7%; adjusted difference, −1.3% [95% CI, −26.3% to 23.7%]), median length of hospital stay (8 d in both groups; adjusted difference, 2.5 [95% CI, −0.9 to 5.8]), and kidney impairment (1% in both groups). Conclusions and Relevance Among older patients with acute heart failure, use of a guideline-based comprehensive care bundle in the ED compared with usual care did not result in a statistically significant difference in the number of days alive and out of the hospital at 30 days. Further research is needed to identify effective treatments for acute heart failure in older patients. Trial Registration ClinicalTrials.gov Identifier: NCT03683212