Recently, a method to determine diuretic responsiveness based on measurements of urinary sodium in the first 6 hours after diuretic administration has been reported. This is a novel concept, and suggests the HF provider could identify poor diuretic responsiveness within 1-2 hours of diuretic administration. This study was conducted in the inpatient setting, where subjects were enrolled up to 4 days after admission. Conducting a similar ED-based study at the time of initial diuretic administration would be important to determine if early diuretic responsiveness can also be predicted using their formula for urinary sodium output. The fractional sodium excretion, (FeNa %), represents the amount of sodium excretion (mmol/time) as a percentage of filtered load [plasma sodium concentration to glomerular filtration rate]. FeNa has been used in several studies to assess diuresis in HF patients. Baseline FeNa has been shown to be reduced to less than 1% in patients with HF and a baseline FeNa of less than 0.2% is associated with diuretic resistance. Identifying effective therapies to mitigate diuretic resistance will improve symptoms, decrease hospital length of stay, conserve healthcare resources and possibly improve morbidity and mortality.