Prolonged QT or QU intervals can be caused by a variety of conditions which include drugs, electrolyte imbalance, and acquired and congenital diseases. This finding is associated with life-threatening ventricular arrhythmias that, at times, have unusual morphologies characteristically named "torsade de pointes." Treatment, when iatrogenic, is obvious--when due to acute acquired diseases, therapy is supportive until the acute phase passes. In congenital prolonged QT syndromes, primidone (Mysoline) recently has been found to be successful in long-term management.