The effects of the volatile anesthetics halothane, enflurane, and isoflurane on amplitude and time variables of contraction and relaxation in isometric, isotonic, and zero-load clamped twitches of isolated right ventricular ferret papillary muscles (n = 24) were compared with those of changing extracellular Ca2+ concentration [( Ca2+]o). Contraction and relaxation variables were compared at equal contraction amplitudes to determine whether the studied anesthetics exert specific effects on contraction and relaxation other than those that may exist as a consequence of their negative inotropic effect. Both changes in [Ca2+]o and anesthetic concentrations had quantitatively and qualitatively similar effects on the following variables of contraction amplitude: peak isometric developed force (DF), maximal extent of shortening (DL), and maximal unloaded velocity of shortening (MUVS). Analysis of anesthetic concentration-effect curves normalized for effects to changes in [Ca2+]o demonstrated that anesthetic effects relative to those of changes in [Ca2+]o were greater on DF greater than DL greater than MUVS. When compared with twitches of equal amplitude in low [Ca2+]o, halothane, enflurane, and isoflurane accelerated isometric and isotonic relaxation. These data are consistent with the hypothesis that the negative inotropic effects of halothane, enflurane, and isoflurane are mostly a consequence of a reduction of intracellular Ca2+ availability and that anesthetic-induced decreases in myofibrillar Ca2+ responsiveness play only a minor role.