(ECG, electrical recording of the heart) changes, have salt imbalance in the blood, especially low concentrations of potassium in the blood (hypokalaemia) which are currently not corrected by treatment, have a very slow heart rate (bradycardia), have a weak heart (heart failure), have a history of abnormal heart rhythms (arrhythmias), or you are taking other medicines that result in certain abnormal ECG changes (see section Taking other medicines).