Holter monitoring was performed in 400 patients undergoing extracorporeal shock wave lithotripsy (ESWL). The highest heart rate occurred before and after ESWL. During respiratory-triggered ESWL, 30% of the patients had one or more ventricular premature beats (VES), and 7% had couplets of VES. The number of ventricular and supraventricular premature contractions was significantly lower during ECG-triggered ESWL. Ventricular tachycardia occurred in seven patients during respiratory-triggered ESWL, and in one patient during nontriggered ESWL. All ventricular tachycardias were nonsustained, asymptomatic, and slow. Supraventricular tachycardia was seen in nine patients. The preference of the urologist for respiratory-triggered ESWL, conflicts with its higher incidence of ventricular arrhythmias.