The overall objective of this study is to further our understanding of electrical phenomena in heart cells. We are particularly interested in the influence of a variety of environmental factors including temperature, pressure, acid-base status and ionic milieu on autorhythmicity excitability and conduction in these cells. A wide range of animal species and cardiac cell types are being studied using experimental techniques including potentiometric measurements of membrane potential, ionic substitution, ion specific blocking agents and voltage clamping. Perturbations in temperature and hydrostatic pressure are being varied as biophysical parameters to gain insight into the thermodynamic nature of membrane excitability. The relative roles of calcium, hydrogen and bicarbonate ions in action potential electrogenesis are being investigated under both normal and abnormal i.e., arrhythmogenic, conditions.