The study evaluates 3 different populations:

It is an open, randomized, parallel-group study comparing the effectiveness of intravenous (iv) ajmaline with currently used antiarrhythmic drugs in the acute treatment of :

1. recent-onset atrial fibrillation versus iv flecainide
2. sustained monomorphous ventricular tachycardia versus iv procainamide

The study also evaluates in an open, randomized, crossover study, the use of iv ajmaline versus iv flecainide in the diagnosis of Brugada syndrome

Inclusion Criteria:

• AF: Patients with isolated, idiopathic, sustained, symptomatic, recent onset(>10 minutes to <24 hours) atrial fibrillation.
• VT: Patients with ventricular tachycardia with good haemodynamic tolerability attending the emergency room or induced at the electrophysiology lab during testing for ventricular arrhythmias.
• Brugada Sd (BrS): First-degree relatives of a patient with Brugada Syndrome with a ECG non-diagnostic of the BrS.

Exclusion Criteria:

• General: Pregnancy
• AF: Pre-existing heart disease.
• Secondary AF
• 2nd and 3rd degree AV block or RBBB associated with LAFB or LPFB (bifascicular block).
• LVF<40%.
• Moderate-severe liver failure.
• AF with haemodynamic compromise.
• VT:VT with haemodynamic compromise.
• BrS:Pre-existing heart disease.
• 2nd and 3rd degree AV block or RBBB associated with LAFB or LPFB (bifascicular block).
• Moderate-severe liver failure.