Eighteen patients with long QT interval and recurrent ventricular tachycardia, torsade de pointe, were studied. Fourteen patients had an underlying heart disease. The factors involved in the appearance of this arrhythmia were: antiarrhythmic drugs (55.5%), complete heart block (33.5%), Romano-Ward syndrome (5.5%) and hypokalemic periodic paralysis (5.5%). In drug-induced torsade de pointe the QT interval was moderately prolonged. Seven patients (70%) had hypokalemia and 5 patients were bradycardic (50%). In patients with heart block-induced torsade de pointe, the QT interval was markedly prolonged. The ventricular rate was markedly slow (38 beat/min +/- 6 SD), and hypokalemia was less obvious (33.3%). In all cases there were ventricular extrasystoles with bigeminy, couplets or polymorphism on the basic ECG. Long-short sequence initiating the torsade de pointe was observed in 83 out of the 92 episodes. The withdrawal of the offensive drug or the correction of a treatable cause was sufficient to prevent torsade de pointe while the use of isoproterenol was effective in 7 patients who received this drug alone or prior to the ventricular pacing which was successfully used in 9 patients. Lidocaine was ineffective or had deleterious effects in 15 patients where electrical cardioversion required repeated use with an average of 5 times/patient.