Ibutilide is a class III antiarrhythmic drug used for pharmacological cardioversion of recent-onset atrial fibrillation and flutter. The objective of the study was to assess the efficacy of ibutilide in elderly patients (age, >or=65 years). The study population consisted of 32 consecutive elderly patients (17 women, 15 men; mean age, 76 +/- 8 years; age range, 65-94 years) with recent-onset atrial fibrillation (19 patients) or flutter (13 patients). Ibutilide was administered 1-mg intravenously over 10 minutes, and a second 10-minute infusion of 1-mg was given if the arrhythmia did not terminate within 10 minutes after the end of initial infusion. Twenty-six patients received two 1-mg doses of ibutilide. The rate of successful arrhythmia termination was 59% (19 patients): 63% in patients with atrial fibrillation (12 of 19) and 54% in atrial flutter (7 of 12). The mean conversion time was 33 +/- 45 minutes. Three-fourths of the conversions occurred within 45 minutes of treatment. No clinical variables were correlated with success of cardioversion. Patients with a left atrial size of 50 mm or larger had a conversion rate of 50% compared with a conversion rate of 61% in patients with a left atrial size of less than 50 mm (P = NS). Ibutilide-induced lengthening in the QTc interval was of 17 +/- 21 milliseconds. Cardiac complications were torsade de pointes (1 patient), nonsustained ventricular tachycardia (1 patient), and transient bradycardia (1 patient). Torsade de pointes was terminated with direct current cardioversion. Ibutilide appears to be an effective drug for conversion of recent-onset atrial fibrillation and flutter in elderly patients under monitored conditions. Complications are rare and transient.