The aim of this work was to analyze the prevalence of level function disorder in patients with atrial fibrillation taking constantly amiodarone. Two groups of patients were studied: in group 1 (n = 78) patients with persistent atrial fibrillation taking constantly amiodarone for rhythm control were included, group 2 (n = 67) consisted of patients with permanent atrial fibrillation taking propafenon, ethacizine and digoxin for rate control. In studied groups liver transaminase activity and data of liver echography after 90 +/- 8 days of treatment were estimated. In 51.58% patients of group 1 asymptomatic increase of liver transaminase activity was found. If liver transaminase activity had been raised before taking amiodarone, frequency and degree of liver transaminase increase extended. Consequently, patients taking constantly amiodarone, require dynamic control of GGTP, AIAT, AsAT once a quarter. If liver transaminase activity increases because of amiodarone taking the method of treatment is possible to be changed and rate control therapy may be chosen.