Fig. 2. (A ) Force–frequency relation under the influence of xenon (n = 12), isoflurane (n = 12), or control (n = 12). The force of contraction is expressed in percent of values taken after equilibration with anesthetic gases at a stimulation frequency of 1 Hz. All groups show a physiologic positive force–frequency relation. There is no significant difference between the control, xenon, or isoflurane groups. (B ) Time to peak tension (TPT) and time to 90% relaxation (TR90) during changing stimulation frequencies under the influence of xenon (n = 12), isoflurane (n = 12), or control (n = 12). All experimental groups show the physiologic shortening of contraction and relaxation at higher pacing rates. In the presence of isoflurane, contraction times were slightly shorter than in control. *P < 0.05 versus control. (C ) TR90during changing stimulation frequencies under the influence of xenon (n = 12), isoflurane (n = 12), or control (n = 12). All experimental groups show the physiologic shortening of contraction and relaxation at higher pacing rates. No significant difference between experimental groups can be detected.