For decades, diuretics have been the cornerstone in the treatment of patients with chronic heart failure with reduced ejection fraction (HFrEF) presenting with congestion. However, evidence guiding the use of diuretics is generally lacking. Adequate dosing and evaluation of diuretic effect are important for treatment success. Measuring the concentration of sodium in urine in addition to urinary output has been suggested as a good marker to guide the use of diuretics. This review summaries the current knowledge on the use of diuretics in patients with HFrEF presenting with congestion.