Ablation of isthmus-dependent atrial flutter in patients previously medicated with antiarrhythmic drugs may cause functional isthmus block during ablation, and subsequent discontinuation of therapy may lead to incomplete isthmus block (and recurrence). This may be particularly important if the drugs previously used have long plasma half-lives (and washout periods). The objective of this study was to evaluate whether the recurrence rate of isthmus-dependent atrial flutter was greater in patients previously medicated with antiarrhythmic drugs and whether there were differences in recurrence rate with different types of antiarrhythmic drugs. During a mean follow-up of 20 +/- 7 months, we observed 57 patients with previous successful ablation of isthmus-dependent atrial flutter. This population of patients was divided into three groups according to the type or absence of previous antiarrhythmic drugs: Group 1--n = 18, patients previously medicated with amiodarone; Group 2--n = 27, patients previously medicated with drugs with short plasma half-lives (propafenone; flecainide; beta-blockers); Group 3--patients without previous antiarrhythmic medication. In all 57 patients bidirectional isthmus block was achieved after the ablation procedure; 8 mm non-irrigated tip catheters were used. During follow-up a recurrence rate of 33% was observed in Group 1 (6 recurrences in 18 patients; p < 0.05 in comparison with Groups 2 and 3); 3.7% in Group 2 (1 in 27 patients) and 0% recurrence rate in Group 3. We conclude that in our study the patients previously medicated with amiodarone had a higher recurrence rate of the arrhythmia compared to patients not previously medicated with antiarrhythmic drugs or medicated with antiarrhythmics with short plasma half-lives.