ABSTRACTChanges in reaction time during the cardiac cycle have been reported by a number of investigators. The present study concerns changes in the latency of alpha blocking as a function of the time of presentation of photic stimulation during the cardiac cycle. Stimuli were presented at intervals of 0, 25, 50, 75, 100, 200, 300, 400, and 500 msec following the peak of the R‐wave of the EKG. Alpha blocking latency was found to be shorter for stimulus presentation early in the cardiac cycl