Using pneumotonometry combined with a Langham ocular blood-flow system, measurements of pulsatile ocular blood flow (POBF) were performed in eight ocular normotensive patients with implanted cardiac pacemakers, with the subjects assuming both the erect and the supine postures. Sequential measurements of POBF were made at pre-set values of heart rate over the physiological range between 60 and 120 beats/min at intervals of 10 beats/min. With patients in the supine position, measurements of cardiac output and stroke volume indices were also recorded by impedance cardiography. The mean pulse amplitude of the intraocular pressure (the ocular pulse) decreased as heart rate increased, and this change was statistically significant in both postures according to repeated-measures analysis of variance (erect: f=18.7, P < 0.0001;="" supine:="">f=18.8, P<0.0001). as="" measured="" in="" supine="" patients="" following="" an="" increase="" in="" heart="" rate,="" the="" pulse="" amplitude="" decreased="" in="" parallel="" with="" a="" decline="" in="" stroke="" volume="" index="">f=18.8, P<0.0001). up="" to="" a="" level="" of="" 90="" beats/min,="" the="" mean="" pobf="" increased="" with="" heart="" rate,="" but="" it="" declined="" above="" this="" rate="" in="" both="" erect="" and="" supine="" postures.="" at="" all="" heart="" rates,="" intraocular="" pressure="" was="" higher="" when="" subjects="" were="" supine="" than="" when="" they="" stood="" erect="">f=4.3, P<0.001). at="" lower="" heart="" rates="" of="" 70="" and="" 80="" beats/min,="" ocular="" pulse="" volume="" and="" pobf="" were="" significantly="" lower="" in="" supine="" patients="" than="" in="" erect="" subjects="" (70="" beats/min:="">t=3.89, P<0.01 vs;="">t=3.87, P<0.01; 80="" beats/min:="">t=2.85, P< 0.05="" vs="" ;="">t = 2.87, P< 0.05).="" we="" conclude="" that="" when="" the="" heart="" rate="" is="" under="" normal="" physiological="" drive,="" the="" decline="" in="" pobf="" that="" accompanies="" the="" act="" of="" lying="" down="" is="" determined="" both="" by="" the="" change="" in="" posture="" itself="" and="" by="" the="" fall="" in="" heart="" rate="" that="" is="" associated="" with="" it.="" these="" observations="" suggest="" a="" possible="" disadvantage="" inherent="" in="" the="" use="" of="" anti-glaucoma="" drugs="" that="" inter="" alia="" induce="">