The study team hypothesizes patients at risk for diuretic resistance can be identified early in their Emergency Department (ED) or hospital stay by evaluating their urine sodium and potassium concentration after an initial dose of IV loop diuretic. The goal of this pilot study is to prospectively study urinary electrolyte excretion and determine patterns of diuretic responsiveness. This study would be utilized to power an interventional study which aims to study alternative methods of treating patients who are identified as having a poor response to diuretics in the ED and hospital. This would be expected to have a significant impact on a patient's hospital course, length of stay and adverse events.