Electrical cardioversion of atrial tachyarrhythmia has disadvantages, such as the need for general anaesthesia, skin burns and thoracic pain. Pharmacodynamic cardioversion is without these side effects, but the reports of the efficacy of the treatment vary a lot. Amiodarone has been the only drug so far reported to give a combination of high efficacy and low frequency of serious side effects such as ventricular tachycardia and shock. The purpose of the present study was to assess the effect of amiodarone on chronic atrial tachycardia. Seventeen patients with chronic atrial fibrillation or flutter were given an oral dose of 30 mg/kg amiodarone. Serial blood tests after amiodarone ingestion were taken to document absorption. Patients, who did not convert to sinus rhythm within 24 hr were treated by electrical cardioversion. No patients converted pharmacodynamically to sinus rhythm. Twelve patients (71%) reached the recommended serum concentration of amiodarone (2-2.5 mg/l, median 2.4 mg/l, range 0.96-4.7). The concentration of desethylamiodarone remained low (<0.2 mg/l), and there were no objective or subjective side effects following the treatment. Sixteen patients (94%) were converted to sinus rhythm the day after by electrical cardioversion without complications. A single high dose of amiodarone is a safe but ineffective method of converting chronic atrial fibrillation and flutter, and may be used as adjuvant therapy in combination with electrical cardioversion.