Figure 2. Effects of 1 minimum alveolar concentration (MAC) isoflurane (n = 8) and 1 MAC sevoflurane (n = 8) on the inotropic effects of phenylephrine (A) or isoproterenol (B). Data are absolute mean values of the active isometric force (AF)+/- SEM. Control groups, n = 10. B1 corresponds to baseline values at a calcium concentration of 0.5 mM. B2 corresponds to baseline values after halogenated anesthetic exposure in the isoflurane and sevoflurane groups. Because the baseline value of AF differs markedly among papillary muscles, it is difficult to show a pharmacologic effect when using absolute values.