The time dependence of cell viability from changes in the electrical impedance ratio of monolayer-cultured rat cardiomyocytes stored at cold temperatures was estimated. Because this ratio varies with temperature, the initial value at 0 h of storage time, which is not equilibrated to the storage temperature, is unknown. Therefore, assuming that the time dependence of cell viability and its ratio during cold storage follows a Weibull distribution, we estimated the initial value of cell viability during cold storage (4, 6°C) and compared it with the actual measured cell viability. Results showed that it was possible to have presumed storage time 0 h (initial value) from the electric impedance ratio in each storage time under cold storage of cells.