In order to compare the differences of high-frequency jet ventilation (HFJV) synchronized with the cardiac cycle (sync) to that nonsynchronized with the cardiac cycle (async), ten stable postoperative ICU patients, without heart failure, in sinus rhythm were ventilated randomly in either mode. The async mode was HFJV at 100 cycle/min, while the sync mode was HFJV triggered by the R-wave of the ECG tracing. The heart rate ranged between 64 and 127 beat/min. Synchronization was studied at one of two periods, sync 0 and sync 60. Sync 0 consisted of inspiration triggered by the R-wave, with jet ventilation occurring early in systole; sync 60 represented a 60% delay of the time between the succeeding R-waves, with jet ventilation occurring in mid-diastole. There was no significant difference in the cardiorespiratory data when async was compared to either sync 0 or sync 60. Therefore, in these patients without heart failure, the selection of async vs. either sync mode appeared to have neither adverse nor beneficial hemodynamic effects.