heart failure (HF) syndromes. The degree of variability and its relationship with length of stay (LOS) is unknown. Hypothesis: We hypothesized that the timeline for initial diuretic administration would vary significantly, based upon multiple patient and system level factors, and later administration would be associated with longer LOS. Methods and Results: From a retrospective cohort of 2171 HF admissions at a single academic medical center, we performed mixed linear regression analyses to assess the relationship between timing of diuretic administration and LOS. We found marked heterogeneity time to diuretic administration with a range of 2 minutes to more than 36 hours after presentation. The median time to administration was 5.1 hours (IQR 2.4,9.5) for the overall population. Fifty one percent of patients (N51107) received the first dose of furosemide in the ED, but in ten percent of these patients the dose was given more then 5 hours after presentation. For those patients that did not receive furosemide in the ED, the median time to administration was 9.3 hours. In the overall population, there was no correlation between timing of treatment and length of stay (r50.015) even after adjusting for multiple confounders (P50.8). Time to initial inpatient diuretic administration was associated with a modest (0.8%) increase in length of stay (95% CI 0.13-1.4%, P50.02) but timing in the ED was not (P50.6). In a secondary analysis, the patients who received any furosemide in the ED sustained a 9% increase in length of stay (P50.003), compared with those who did not receive furosemide in the ED. Conclusions: Timing of initial diuretic treatment is variable and likely reflective of the continued diagnostic challenge in acute HF patients. Our study suggests rapid diuretic administration in the ED may not be universally beneficial and that delay in treatment until further testing is available as an inpatient may be warranted. More data are needed to decide whether improved diagnostic tools would facilitate diagnosis and potentially help to standardize care for HF patients in the emergency department.