Circulatory effects in healthy young men of atrial pacing at rest and during isometric handgrip.

1. The influence of a fixed heart rate and cardiac output on the cardiovascular response to isometric handgrip at one third of maximal voluntary contraction has been studied by means of atrial pacing. 2. At rest, atrial pacing with a mean heart rate of 109 beats/min increased cardiac output and forearm blood flow while total systemic and forearm vascular resistance decreased. 3. During handgrip, total systemic resistance increased both with and without pacing. A slow lowering of forearm vascular resistance was noted in the former situation, no change in the latter. 4. It is concluded that atrial pacing per se increases cardiac output in healthy, young volunteers. Handgrip elicits a vasoconstriction on other vascular beds than the resting forearm.