The antiarrhythmogenic effect of the flavonoid dioclein on myocardial ischemia/reperfusion was investigated in isolated perfused rat hearts. Low concentrations of dioclein (30-300 nM) induced a reduction of arrhythmias observed during the reperfusion period. Dioclein also preserved the diastolic tension after reperfusion without affecting the systolic tension. In addition, dioclein (150 nM) dramatically reduced the formation of reactive oxygen species (ROS) observed during reperfusion in hearts. In conclusion, dioclein acts as a potent antiarrhythmogenic and antioxidant drug with an excellent protective effect during reperfusion of ischemic hearts.