Recent advances in cardiac electrophysiology have allowed for the preparation of viable single frog atrial cells. These cells have properties which make them ideal for voltage clamp studies. The ionic currents observed under voltage clamp conditons from single frog atrial cells are analyzed with the use of automatic methods programmed on a computer. From the analyzed data, mathematical models are formed which describe the time and voltage dependence of the various ionic currents observed under voltage clamp conditions. These models are then combined, and a membrane action potential is reconstructed based on the analyzed ionic current data. This membrane action potential is then used as input to a nonlinear least-squares fitting routine in an attempt to accurately fit the model to experimental action potential data.