Renal digoxin clearance was compared in patients suffering from atrial fibrillation with well preserved cardiac function (n=9; salt intake ±170 mmol daily) and patients with chronic congestive heart failure (n=10; salt intake 50 mmol daily and maintenance treatment with diuretics). There was no difference between the groups concering digoxin dosage, creatinine clearance, diuresis or sodium excretion in the urine. Digoxin clearance in chronic heart failure proved to be significantly lower than in atrial fibrillation (48±21 vs 71±36 ml·min^–1, p<0.05), and="" cdig/ccreat="" was="" similarly="" reduced="" at="" 0.73±0.15="" compared="" to="" 1.09±0.27="">p<0.005). steady="" state="" serum="" digoxin="" concentration="" was="" significantly="" higher="" in="" patients="" with="" congestive="" heart="" failure="" (1.44±0.47="" vs="" 0.87±0.33="">^–1, p<0.01). chronic="" congestive="" heart="" failure="" is="" a="" state="" with="" reduced="" digoxin="" clearance="" by="" the="" kidney,="" which="" could="" lead="" to="" digoxin="" intoxication="" not="" explicable="" by="" overdose,="" reduced="" renal="" function="" or="" the="" effect="" of="" interacting="">