Extracorporal lithotripsy has transformed the treatment of renal stones. However, the shock waves can generate arrhythmias which may be severe. To prevent them, the shocks were synchronised to the absolute refractory period of the cardiac cycle with a corollary, an increase in the procedure time. The latest generation of lithotriptors have a number of technical improvements allowing desynchronisation but with a high theoretic risk of arrhythmias. The aim of this study was to assess the arrhythmogenic effects of desynchronised shocks by Holter ECG monitoring during the procedure. This was a prospective randomised study: 25 patients with no previous cardiovascular history were included: 15 men and 10 women with a mean age of 45 years. The originality of this study was the delivery of shock waves in two phases (synchronised versus desynchronised) in a random fashion, the order being unknown to the cardiologist interpreting the recordings. In the synchronised mode, none of the patients developed an arrhythmia. On the other hand, in the desynchronised mode, hyperexcitability was observed in 7 patients, supraventricular in 6 cases (atrial extrasystoles and atrial doublets) and ventricular in 4 cases (VES, ventricular doublets and 1 unsustained ventricular tachycardia). These arrhythmias were asymptomatic and regressed spontaneously. The authors conclude that although they are arrhythmogenic, desynchronised procedures with the latest lithotriptors are acceptable, provided that the patients undergo a cardiological examination beforehand to identify high risk patients and that there is adequate monitoring during the procedure in the presence of an anaesthetist.