“…Since Gaskell's early observation (7), many reports (3,6,8,9,11,14,15,(17)(18)(19) have examined and discussed the nature of the post-pacing pause which is now commonly thought to be due to overdrive suppression (14,26). Because measurement of sinus node recovery time (SNRT) is one of the most common clinical and experimental electrophysiological tests of sinus node function (8,11,14,15,17,23), it is important to know which variables will influence SNRT and how they will do so. Numerous studies have shown that SNRT varies with the pacing rate (11,14,15,19,28), the duration of pacing (9,11,14), the stimulus strength (3,29), the spontaneous rate (6,15,20,25) and neurohumoral influences (2,9,11,14), but in each of these studies each variable was examined independently (6,9,11,14,28), thus precluding an overall assessment of the interrelationships between variables and between each variable and SNRT.…”