The effects of dronedarone, a non-iodinated derivative of amiodarone, on 
ventricular tachycardia and ventricular fibrillation post-myocardial infarction 
are not well established. Fifty-five Wistar rats were randomly allocated to a 
2-week oral treatment with either vehicle (n=18), amiodarone (30 mg/kg, n=20), 
or dronedarone (30 mg/kg, n=17). After acute coronary artery ligation, a 
single-lead electrocardiogram was continuously recorded for 24 h and episodes of 
ventricular tachycardia/fibrillation as well as mortality rates were analysed. 
Monophasic action potential recordings were obtained from the left ventricular 
epicardium at baseline and 24 h post-myocardial infarction. Thyroid hormones and 
catecholamines were measured using radioimmunoassay. Thyroid function was 
similar in the 3 groups. Compared to controls, amiodarone and dronedarone 
equally decreased the number of ventricular tachycardia/fibrillation episodes by 
approximately 75%. Both agents prevented the increase in monophasic action 
potential duration and in beat-to-beat variation. Norepinephrine levels were 
lower only after amiodarone treatment. Despite the observed antiarrhythmic 
effect, total mortality did not differ between groups (38.8% in controls, 30.0% 
in the amiodarone group and 58.8% in the dronedarone group), because of excess 
bradyarrhythmic mortality in both drug groups that reached significance in the 
dronedarone group. Dronedarone and amiodarone display similar antiarrhythmic 
efficacy post-myocardial infarction, partly by preventing repolarization 
inhomogeneity. However, dronedarone increases bradyarrhythmic mortality possibly 
secondary to its negative inotropic effects.