We have developed a mathematical model of a rabbit ventricular cell based on available whole cell voltage clamp data. The model consists of three components: a Hodgkin-Huxley type membrane model describing the electrical activity of the cell membrane; and intracellular fluid compartment model; and a small extracellular cleft space. Material balances for Na+, K +, and Ca2+ provide the describing equations for the intra and extracellular spaces. A model for the sarcoplasmic reticulum is also provided in the intracellular fluid compartment model. Whole cell voltage clamp data from the rabbit ventricular myocyte was utilized to characterize the kinetics of the ionic membrane currents. Parameters associated with the ionic currents can be adjusted to yield good fits to measured action potential and Ca2+ transient waveforms recorded in our laboratory. Moreover, the model can be employed to qualitatively predict the ionic mechanisms underlying repolarization.