Purpose: We examine the effects of fixed rate shock wave administration on the cardiac rhythm and treatment efficacy of a tubless lithotriptor (Dornier MFL 5000* * Dornier Medical Systems, Marietta, Georgia. ). A secondary goal was to examine the treatment efficacy of fixed shock were administration compared to R wave triggered lithotripsy. Materials and Methods: In this prospective study Holter monitoring was used before, during and after nonR wave triggered shock wave lithotripsy. Results: An increase in premature ventricular contractions was noted during shock wave lithotripsy. However, there were no episodes of significant ventricular ectopia, ventricular tachycardia, asystole or heart block as a result of nonR wave triggered shock wave administration. NonR wave gated shock wave lithotripsy expedited patient treatment (mean treatment time 46 plus/minus 21 minutes), minimized the use of sedation during treatment and produced results similar to R wave gated shock wave lithotripsy with the MFL 5000 lithotriptor. Conclusions: With adequate precautions, fixed rate shock wave administration would appear to be a reasonable option to treat urolithiasis with the MFL 5000 lithotriptor as with other newer lithotriptors.