Vaughan-Williams classification of anti-arrhythmic drugs:
| Ia | Moderate depression of phase 0 and conduction slowing; prolongation of repolarisation (eg quinidine ) |
| Ib | Minimal effect on phase 0 and on conduction properties; shortening of repolarisation (eg lidocaine ) |
| Ic | Marked depression of phase 0 and conduction slowing; slight effect on repolarisation (eg fleainide ) |
| II | Beta-adrenergic blockade (eg propranolol ) |
| III | Lengthening of repolarisation (eg amiodarone ) |
| IV | CaIcium channel blockade (eg verapamil ) |