Arrhythmias are caused by the interdependent processes of change in energy metabolism and alterations in sarcolemmal ion gradients that occur during ischemia. Depletion of energy metabolites and increased proton concentrations in ischemic heart may underlie the observed phenomena of reduced contractile force and also of malignant ventricular arrhythmias that can lead to tachycardia and ventricular fibrillation. Recent advances in measuring changes in ion concentrations and metabolites during cardiac ischemia have provided a wealth of detail on the processes involved. Some of the experimental data have been used to construct a computer model that integrates cardiac energetics with electrophysiological changes. This is a novel approach to studying myocardial ischemia, and the resulting model would aid in the prediction of the effects of therapeutic interventions.