The present study investigated the effects of dronedarone and amiodarone on 
plasma thyroid hormones and the possible consequences on the response of the 
heart to ischemia. Amiodarone (30 mg/kg/day per os) or dronedarone (30 mg/kg/day 
per os) were administered for 2 weeks in normal and thyroxine-treated animals 
(25 microg/100 g body weight od sc, for 2 weeks), while animals without 
amiodarone and dronedarone served as controls. Isolated rat hearts were perfused 
in a Langendorff mode and subjected to 20 and 30 min of zero-flow global 
ischemia followed by 45 min of reperfusion. Functional changes were assessed by 
measuring left ventricular developed pressure (LVDP) under resting conditions 
and in response to ischemia-reperfusion, LVDP%, as well as the severity of 
ischemic contracture. Amiodarone resulted in increased T4, T4/T3 and rT3, 
whereas dronedarone did not alter the thyroid hormone profile in normal animals. 
In thyroxine-treated animals, amiodarone increased T4/T3 ratio but T4, T3 and 
rT3 levels were not altered. Basal functional parameters and ischemic 
contracture did not change by amiodarone and/or dronedarone neither in normal 
nor in thyroxine-treated hearts. In normal hearts, postischemic functional 
recovery, LVDP%, was not altered by amiodarone or dronedarone administration. 
LVDP% was statistically higher in thyroxine-treated hearts than in normal and 
this beneficial effect was not abolished by amiodarone or dronedarone treatment.