AimsTo study loop diuretic response and effect of loop diuretic omission in ambulatory heart failure (HF) patients on chronic low‐dose loop diuretics.Methods and resultsUrine collections were performed on two consecutive days in 40 ambulatory HF patients with 40–80 mg furosemide (day 1 with loop diuretic; day 2 without loop diuretic). Three phases were collected each day: (i) first 6 h; (ii) rest of the day; and (iii) night. On the day of loop diuretic intake, the total natriuresis was 125.9 (86.9–155.0) mmol/24 h and urine output was 1650 (1380–2025) mL/24 h. There was a clear loop diuretic response with a natriuresis of 9.4 (6.7–15.9) mmol/h and a urine output of 117 (83–167) mL/h during the first 6 h, followed by a significant drop in natriuresis and urine output during the rest of the day [2.6 (1.8–4.8) mmol/h and 55 (33–71) mL/h] and night [2.2 (1.6–3.5) mmol/h and 44 (34–73) mL/h]. On day 2, after loop diuretic omission, the natriuresis and urine output remained similarly low the entire day, resulting in a 50% reduction in natriuresis [55.1 (33.5–77.7) mmol/24 h; P < 0.001] and a 31% reduction in urine output [1035 (875–1425) mL/24 h; P < 0.001] compared with the day of loop diuretic intake.ConclusionPatients with HF on chronic loop diuretic treatment still have a clear diuretic response phase, while loop diuretic omission leads to a significant drop in natriuresis and urine output, arguing against routine cessation of low‐dose loop diuretics.