A method is presented that consistently yields a large number of calcium-tolerant myocytes from mammalian, amphibian, and elasmobranch hearts and from mammalian stomach. The use of incubating solutions or cell harvesting techniques was not required. The time needed to isolate cells was shorter than previously reported values. Action potentials recorded from each cell type appear similar in configuration to that of the intact multicellular tissue. The isolated myocytes appear to tolerate long periods of electrophysiological experimentation using the "giga-seal" suction electrode technique of Hamill et al. (Pfluegers Arch. 391: 85-100, 1981). This method is ideally suited for comparative electrophysiological studies, since the procedure for cell isolation was not seriously modified according to the preparation or species used.