We measured left-ventricular (LV) systolic time intervals (STI) to determine whether breath-holding and simulated diving evoke a depression of LV performance in man similar to that previously demonstrated in natural divers. Records of STI were obtained by a noninvasive procedure in 15 adult males who had breath-holding diving experience during supine rest, at 30 and 60 s of simple breath-holding (BH) and at 30 and 60 s of BH combined with cold, wet facial stimulation (FS). Changes in both BP and HR during FS reflected cardiovascular behavior typical of simulated diving. The isovolumic contraction period increased 13% and 31% after 60 s of BH and FS, respectively. LV ejection time shortened by 30 ms during BH and by 37 ms during FS. These measurements of STI represent the first description of cardiac cycle components during the human diving response. The alterations in STI suggest that a reduction in LV performance, as seen by a decreased rate of preejection pressure development and a diminished stroke volume, had occurred during the apneic maneuvers. In addition, there was a trend in these measures indicating that FS potentiated the response over that which occurred during BH. Thus, it appears that man exhibits a depression of LV performance during simulated diving similar to that found in natural divers.