Mechanisms of Diuretic Resistance in Heart Failure, Aim 1

Inclusion Criteria: * Clinical diagnosis of HF * No plan for titration/change of heart failure medical or device therapies during the study period. * Absence of non-elective hospitalizations in the previous 3 months. * At optimal volume status by symptoms, exam, and dry weight * Age \> 18 years Exclusion Criteria: * GFR \<20 ml/min/1.73m2 using the Chronic Kidney Disease- Epidemiology (CKD-EPI)equation or use of renal replacement therapies * Use of any non-loop type diuretic in the last 14 days with the exclusion of low dose aldosterone antagonist (e.g., spironolactone or eplerenone ≤50 mg). Examples of non-loop diuretics include but may not be limited to acetazolamide (oral or IV, not ophthalmic), metolazone, Hydrochlorothiazide (HCTZ), chlorthalidone, chlorothiazide, indapamide, triamterene, amiloride, finerenone, spironolactone dose \> 50mg day, eplerenone \> 50mg/day, * History of flash pulmonary edema requiring hospitalization and treatment with biphasic positive airway pressure or mechanical ventilation or a "brittle" volume sensitive HF phenotype such as an infiltrative or restrictive cardiomyopathy (i.e. amyloid cardiomyopathy, etc). * Hemoglobin \< 8 g/dL * Pregnant or breastfeeding * Inability to give written informed consent or comply with study protocol or follow-up visits * Chronic Urinary retention limiting ability to perform timed urine collection procedures