We compared the responses to a Mueller maneuver maintained for 20 s to effects of an equal period of end expiratory apnea. We measured heart rate, mean blood pressure (BP), central venous pressure (CVP), and sympathetic nerve activity (SNA) in 9 normal humans. The Mueller maneuver was accompanied by a fall in CVP from 5 +/- 1.2 to -13 +/- 3.2 mmHg (P < 0.05). During the first 10 s of Mueller, BP fell from 95 +/- 4.2 to 81 +/- 5.5 mmHg and SNA fell as low as 16 +/- 6% of control (P < 0.05). For the 5 s prior to release SNA increased to 236 +/- 36% (P < 0.05), and BP began to increase. Release of the Mueller resulted in a surge in BP to 104 +/- 5.8 mmHg and suppression of SNA to 61 +/- 48% (P < 0.05). By contrast, there was no fall in BP or CVP during apnea and SNA increased to 188 +/- 24% for the first 5 s. Between 16 and 20 s of apnea SNA was 231 +/- 52% and BP increased from 92 +/- 3.1 to 96 +/- 3.6 mmHg (P < 0.05). Release of apnea resulted in a surge in BP to 105 +/- 3.0 mmHg and suppression of SNA to 30 +/- 12% (P < 0.05). Oscillations in BP and SNA during the Mueller maneuver may contribute to similar oscillations, and hence cardiovascular consequences, in patients with sleep apnea.